Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Mar. 31, 2018	Apr. 30, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	ALPHA & OMEGA SEMICONDUCTOR Ltd
Entity Central Index Key	0001387467
Current Fiscal Year End Date	--06-30
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Common Stock, Shares Outstanding		23,879,992

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Current assets:
Cash and cash equivalents	$ 125,207	$ 115,708
Restricted cash	239	221
Accounts receivable, net	28,927	28,410
Inventories	90,472	76,254
Other current assets	17,115	4,883
Total current assets	261,960	225,476
Property, plant and equipment, net	258,795	148,191
Intangible assets, net	16,619	282
Deferred income tax assets - long-term	4,643	4,594
Other long-term assets	52,830	19,865
Total assets	594,847	398,408
Current liabilities:
Accounts payable	78,079	63,134
Accrued liabilities	61,617	28,386
Income taxes payable	185	1,748
Short term debt	2,130	0
Deferred margin	1,530	814
Capital leases	857	828
Total current liabilities	144,398	94,910
Long-term debt	10,883	0
Income taxes payable - long-term	753	922
Deferred income tax liabilities	2,070	2,659
Capital leases - long-term	214	866
Other long-term liabilities	334	502
Total liabilities	158,652	99,859
Commitments and contingencies (Note 10)
Preferred shares, par value $0.002 per share:
Authorized: 10,000 shares, issued and outstanding: none at March 31, 2018 and June 30, 2017	0	0
Common shares, par value $0.002 per share:
Authorized: 100,000 shares, issued and outstanding: 30,192 shares and 23,852 shares, respectively at March 31, 2018 and 29,600 shares and 23,992 shares, respectively at June 30, 2017	60	59
Treasury shares at cost, 6,340 shares at March 31, 2018 and 5,608 shares at June 30, 2017	(61,710)	(49,836)
Additional paid-in capital	215,168	206,332
Accumulated other comprehensive income	5,154	306
Retained earnings	121,621	113,909
Total Alpha and Omega Semiconductor Limited shareholder's equity	280,293	270,770
Noncontrolling interest	155,902	27,779
Total equity	436,195	298,549
Total liabilities and equity	$ 594,847	$ 398,408

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2018	Jun. 30, 2017
Common shares, par value (in dollars per share)	$ 0.002	$ 0.002
Common shares, authorized (in shares)	100,000,000	50,000,000
Common stock, shares issued (in shares)	30,192,000	29,600,000
Common stock, shares outstanding (in shares)	23,852,000	23,992,000
Preferred stock, par value (in dollars per share)	$ 0.002	$ 0.002
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Treasury shares (in shares)	6,340,000	5,608,000

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenue	$ 102,902	$ 93,281	$ 311,656	$ 285,330
Cost of goods sold	75,769	70,584	228,911	218,595
Gross profit	27,133	22,697	82,745	66,735
Operating expenses
Research and development	9,966	7,625	27,393	21,928
Selling, general and administrative	16,486	12,067	46,857	35,224
Total operating expenses	26,452	19,692	74,250	57,152
Operating income	681	3,005	8,495	9,583
Interest income and other loss, net	(234)	(74)	(354)	(193)
Interest expense	(105)	(22)	(136)	(72)
Net income before income taxes	342	2,909	8,005	9,318
Income tax expense	830	523	32	2,845
Net income (loss) including noncontrolling interest	(488)	2,386	7,973	6,473
Net loss attributable to noncontrolling interest	(2,139)	(1,170)	(5,269)	(3,237)
Net income attributable to Alpha and Omega Semiconductor Limited	$ 1,651	$ 3,556	$ 13,242	$ 9,710
Net income per common share attributable to Alpha and Omega Semiconductor Limited
Basic (in dollars per share)	$ 0.07	$ 0.15	$ 0.55	$ 0.42
Diluted (in dollars per share)	$ 0.07	$ 0.14	$ 0.53	$ 0.39
Weighted average number of common shares attributable to Alpha and Omega Semiconductor Limited used to compute net income per share
Basic (in shares)	23,795	23,675	23,914	23,396
Diluted (in shares)	24,755	24,951	24,916	24,781

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Net income (loss) including noncontrolling interest	$ (488)	$ 2,386	$ 7,973	$ 6,473
Other comprehensive income, net of tax
Foreign currency translation adjustment	5,198	693	9,246	(1,563)
Comprehensive income	4,710	3,079	17,219	4,910
Noncontrolling interest	360	(937)	(871)	(4,069)
Comprehensive income attributable to Alpha and Omega Semiconductor Limited	$ 4,350	$ 4,016	$ 18,090	$ 8,979

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net income (loss) including noncontrolling interest	$ 7,973	$ 6,473
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	21,818	20,148
Share-based compensation expense	8,477	4,585
Deferred income taxes, net	(638)	6,558
Loss (Gain) on disposal of property and equipment	26	(444)
Changes in assets and liabilities:
Accounts receivable, net	(517)	4,142
Inventories	(14,218)	(4,501)
Other current and long-term assets	(16,255)	(6,134)
Accounts payable	6,492	(1,711)
Income taxes payable	(1,731)	(68)
Accrued and other liabilities	2,830	52
Net cash provided by operating activities	14,257	29,100
Cash flows from investing activities
Purchases of property and equipment excluding JV Company	(35,585)	(16,163)
Purchases of property and equipment in JV Company	(87,088)	(15,857)
Purchases of land use rights in JV Company	0	(8,737)
Purchase of intangible assets	(14,034)	0
Proceeds from sale of property and equipment	6	602
(Increase) decrease in restricted cash	(18)	7
Net cash used in investing activities	(136,719)	(40,148)
Cash flows from financing activities
Proceeds from investment by noncontrolling interest	128,994	33,000
Withholding tax on restricted stock units	(2,248)	(1,915)
Proceeds from exercise of stock options and ESPP	2,700	8,958
Payment for repurchases of common shares	12,016	0
Proceeds from borrowings	13,150	0
Principal payments on capital leases	(623)	(622)
Net cash provided by financing activities	129,957	39,421
Effect of exchange rate changes on cash and cash equivalents	2,004	3
Net increase in cash and cash equivalents	9,499	28,376
Cash and cash equivalents at beginning of period	115,708	87,774
Cash and cash equivalents at end of period	125,207	116,150
Supplemental disclosures of non-cash investing and financing information:
Property and equipment purchased but not yet paid	66,563	9,620
Re-issuance of treasury stock	$ 50	$ 7

Intangible assets, net (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 19,051	$ 2,666
Less: accumulated amortization	(2,701)	(2,653)
License fees
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	17,633	1,248
Trade name
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	268	268
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 1,150	$ 1,150

The Company and Significant Accounting Policies	9 Months Ended
The Company and Significant Accounting Policies	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Significant Accounting Policies	The Company and Significant Accounting Policies The Company Alpha and Omega Semiconductor Limited and its subsidiaries (the “Company,” "AOS," "we" or "us") design, develop and supply a broad range of power semiconductors. The Company's portfolio of products targets high-volume applications, including personal computers, flat panel TVs, LED lighting, smart phones, battery packs, consumer and industrial motor controls and power supplies for TVs, computers, servers and telecommunications equipment. The Company conducts its operations primarily in the United States of America (“USA”), Hong Kong, China, Taiwan, Korea, Germany and Japan. Basis of Preparation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) for interim financial information and with the instructions to Article 10 of Securities and Exchange Commission Regulation S-X, as amended. They do not include all information and footnotes necessary for a fair presentation of financial position, results of operations and cash flows in conformity with U.S. GAAP for complete financial statements. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Company’s Annual Report on Form 10-K for the fiscal year ended June 30, 2017. All significant intercompany balances and transactions have been eliminated in consolidation. In the opinion of management, all adjustments (consisting of normal recurring adjustments and accruals) considered necessary for a fair presentation of the results of operations for the periods presented have been included in the interim periods. Operating results for the nine months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the fiscal year ending June 30, 2018. The condensed consolidated balance sheet at June 30, 2017 is derived from the audited financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended June 30, 2017. Joint Venture In March 2016, the Company executed an agreement with two strategic investment funds owned by the Municipality of Chongqing, China (the "Chongqing Funds") to form a joint venture for a new state-of-the-art power semiconductor packaging, testing and wafer fabrication facility in Liangjiang New Area of Chongqing (the "Joint Venture"). The initial capitalization of the Joint Venture under the agreement is $330.0 million, which includes cash contributions from the Chongqing Funds and contributions of cash, equipment and intangible assets from the Company. The Company owns 51% and the Chongqing Funds own 49% of the equity interest of the Joint Venture. The Joint Venture is accounted under the provisions of the consolidation guidance since the Company has a controlling financial interest. Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires the Company to make estimates, judgments and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses. To the extent there are material differences between these estimates and actual results, the Company's condensed consolidated financial statements will be affected. On an ongoing basis, the Company evaluates the estimates, judgments and assumptions including those related to stock rotation returns, price adjustments, allowance for doubtful accounts, inventory reserves, warranty accrual, income taxes, share-based compensation, and useful lives for property, plant and equipment and intangible assets. Fair Value of Financial Instruments The fair values of cash equivalents are based on observable market prices and have been categorized in Level 1 in the fair value hierarchy. Cash equivalents consist primarily of short term bank deposits. The carrying values of financial instruments such as cash and cash equivalents, accounts receivable and accounts payable approximate their carrying values due to their short-term maturities. Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. The Company's accumulated other comprehensive income (loss) consists of cumulative foreign currency translation adjustments. Total comprehensive income (loss) is presented in the condensed consolidated statements of comprehensive income (loss). Recent Accounting Pronouncements In May 2017, the FASB issued ASU 2017-09, "Compensation -Stock Compensation: Scope of Modification Accounting ("ASU 2017-09"). ASU 2017-09 is an update to the existing guidance to clarify when modification accounting would be applied for a change to the terms or conditions of a share-based award. Under this new guidance, modification accounting is required only if the fair value, a vesting condition, or the classification of the award changes as a result of the change in terms or conditions. This ASU will be effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017 with early adoption permitted. The Company does not regularly modify the terms and conditions of its share-based awards and does not expect the adoption of this guidance to have a significant impact on its financial statements. In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows: Restricted Cash ("ASU 2016-18"). ASU 2016-18 requires amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. This ASU will be effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted and requires retrospective adoption. The Company does not expect the adoption of this guidance will have a material impact on its consolidated financial position, results of operations or cash flows. In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"). ASU 2016-15 identifies how certain cash receipts and cash payments are presented and classified in the Statement of Cash Flows under Topic 230. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. Upon adoption, entities must apply the guidance retrospectively to all periods presented. The Company is currently evaluating the impact the adoption of ASU 2016-15 will have on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases. This guidance requires a dual approach for lessee accounting under which a lessee will account for leases as finance leases or operating leases. Both finance and operating leases will result in the lessee recognizing a right-of-use asset and a corresponding liability on its balance sheet, with differing methodology for income statement recognition. This guidance is effective for public business entities for fiscal years, and interim periods within those years, beginning after December 15, 2018, and early adoption is permitted. A modified retrospective approach is required for all leases existing or entered into after the beginning of the earliest comparative period in the consolidated financial statements. The Company is currently assessing the impact that adoption of this guidance will have on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (ASC 606). The standard provides companies with a single model for use in accounting for revenue arising from contracts with customers and supersedes current revenue recognition guidance, including industry-specific revenue guidance. The core principle of the model is to recognize revenue when control of the goods or services transfers to the customer, as opposed to recognizing revenue when the risks and rewards transfer to the customer under the existing revenue guidance. The Company will adopt the new revenue standard on July 1, 2018 utilizing the modified retrospective method. Upon adoption on July 1, 2018, the Company will record a cumulative effect to retained earnings related to deferred revenue balance due to the change in revenue recognition for its two U.S.-based distributors as discussed below. The Company does not expect the cumulative effect adjustment to have a material impact on its consolidated financial statements. The amount as previously disclosed in our annual financial statements was a net amount of $0.8 million as of June 30, 2017 and the Company does not expect the balance as of June 30, 2018 to be materially different. The Company is in the process of finalizing its assessment and implemented policies, processes, and controls to support the standard measurement and disclosure requirements. Under ASC 606, the Company's product sales consist of a single performance obligation that is satisfied at a point in time. The Company recognizes product revenue from distributors and other customers when the products are shipped or delivered to the customers based on the terms of the purchase orders and sales agreements, primarily because the distributors and customers have legal title and physical possession of the product; can direct the use of the product; are obligated to pay the Company for the product; and bear significant risks and rewards of ownership of the products. The change for the Company under ASC 606 relates to the timing of revenue recognition with two U.S.-based distributors. Sales to these distributors are governed under the terms of agreements providing extended price protection and other return rights. Under current accounting standards, revenue and costs related to these sales are deferred until distributors sold to the end customers and the amount of price adjustments is fixed and finalized. Under ASC 606, the transaction price takes into consideration the effect of variable consideration such as price adjustments and returns rights, which are estimated and recorded at the time the goods are delivered. Accordingly, the Company will recognize revenue at the time of shipment or delivery to these two distributors, adjusted for estimates of the price adjustments and product returns based on historical data and other available information. Revenue from other non-U.S. distributors and direct customers, which consists of majority of the Company's total revenue, is currently recognized at the time of shipment or delivery to the distributors and direct customers, Accordingly, revenue recognition with these distributors and direct customers remains unchanged upon adoption of ASC 606.

Net Income (Loss) Per Share

9 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Net Income (Loss) Per Share

Net Income Per Common Share Attributable to Alpha and Omega Semiconductor Limited

The following table presents the calculation of basic and diluted net income per share attributable to common shareholders:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands, except per share data)
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$	1,651	$	3,556	$	13,242	$	9,710

Denominator:
Basic:
Weighted average number of common shares used to compute basic net income per share	23,795		23,675		23,914		23,396
Diluted:
Weighted average number of common shares used to compute basic net income per share	23,795		23,675		23,914		23,396
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	960		1,276		1,002		1,385
Weighted average number of common shares used to compute diluted net income per share	24,755		24,951		24,916		24,781
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic	$	0.07	$	0.15	$	0.55	$	0.42
Diluted	$	0.07	$	0.14	$	0.53	$	0.39

The following potential dilutive securities were excluded from the computation of diluted net income per share as their effect would have been anti-dilutive:



	Three Months Ended March 31,		Nine Months Ended March 31,
	2018	2017	2018	2017
	(in thousands)		(in thousands)
Employee stock options and RSUs	165	3	167	83
ESPP	381	20	157	12
Total potential dilutive securities	546	23	324	95

Concentration of Credit Risk and Significant Customers

9 Months Ended

Mar. 31, 2018

Risks and Uncertainties [Abstract]

Concentration of Credit Risk and Significant Customers

The Company manages its credit risk associated with exposure to distributors and direct customers on outstanding accounts receivable through the application and review of credit approvals, credit ratings and other monitoring procedures. In some instances, the Company also obtains letters of credit from certain customers.

Credit sales, which are mainly on credit terms of 30 to 60 days, are only made to customers who meet the Company's credit requirements, while sales to new customers or customers with low credit ratings are usually made on an advance payment basis. The Company considers its trade accounts receivable to be of good credit quality because its key distributors and direct customers have long-standing business relationships with the Company and the Company has not experienced any significant write-offs of accounts receivable in the past. The Company closely monitors the aging of accounts receivable from its distributors and direct customers, and regularly reviews their financial positions, when available.

Summarized below are individual customers whose revenue or accounts receivable balances were more than 10% of the respective total consolidated amounts:



	Three Months Ended March 31,				Nine Months Ended March 31,
Percentage of revenue	2018		2017		2018		2017
Customer A	25.9	%	27.3	%	28.1	%	26.2	%
Customer B	37.0	%	36.6	%	34.8	%	36.3	%
Customer C	*		10.5	%	*		11.7	%

* Less than 10%



	March 31, 2018		June 30, 2017
Percentage of accounts receivable	March 31, 2018		June 30, 2017
Customer A	19.9	%	33.2	%
Customer B	29.3	%	13.2	%
Customer C	11.9	%	16.4	%

Balance Sheet Components

9 Months Ended

Mar. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Accounts receivable, net:



	March 31, 2018			June 30, 2017
	(in thousands)
Accounts receivable	$	49,607		$	48,039
Less: Allowance for price adjustments	(20,650		)	(19,599		)
Less: Allowance for doubtful accounts	(30		)	(30		)
Accounts receivable, net	$	28,927		$	28,410

Inventories:



	March 31, 2018		June 30, 2017
	(in thousands)
Raw materials	$	45,295	$	32,118
Work in-process	36,252		36,081
Finished goods	8,925		8,055
	$	90,472	$	76,254

Other current assets:



	March 31, 2018		June 30, 2017
	(in thousands)
VAT receivable	$	12,979	$	591
Other prepaid expenses	2,438		2,171
Prepayment to supplier	611		148
Prepaid income tax	536		1,356
Other receivable	551		617
	$	17,115	$	4,883

Property, plant and equipment, net:



	March 31, 2018			June 30, 2017
	(in thousands)
Land	$	4,877		$	4,877
Building	4,325			4,325
Manufacturing machinery and equipment	250,341			215,275
Equipment and tooling	15,098			13,549
Computer equipment and software	25,310			24,346
Office furniture and equipment	2,150			1,935
Leasehold improvements	29,740			29,136
Land use rights	9,566			8,849
	341,407			302,292
Less: accumulated depreciation	(222,568		)	(194,882		)
	118,839			107,410
Equipment and construction in progress	139,956			40,781
Property, plant and equipment, net	$	258,795		$	148,191

Intangible assets, net:



	March 31, 2018			June 30, 2017
	(in thousands)
License fees	$	17,633		$	1,248
Trade name	268			268
Customer relationships	1,150			1,150
	19,051			2,666
Less: accumulated amortization	(2,701		)	(2,653		)
	16,350			13
Goodwill	269			269
Intangible assets, net	$	16,619		$	282

Intangible assets of license fees are primarily related to a license agreement that the Company entered into with STMicroelectronics International N.V. (“STMicro”) on September 5, 2017, pursuant to which STMicro granted the Company a world-wide, royalty-free and fully-paid license to use its technologies to develop, market and distribute certain digital multi-phase controller products, which have been offered by STMicro. This agreement allows the Company to develop and market products in a new market, primarily in the computer server segment. Under the license agreement, the Company agreed to pay a total price in cash of $17.0 million based on the payment schedule of approximately $10.1 million, $6.7 million, $0.2 million in calendar year 2017, 2018 and 2019, respectively. As of March 31, 2018, the Company recorded $16.4 million in intangible assets, of which $13.5 million in cash was paid to STMicro. The Company begins amortizing such license fees when the technology has met the Company's qualification.

Other long-term assets:



	March 31, 2018		June 30, 2017
	(in thousands)
Prepayments for property and equipment	$	47,523	$	12,964
Investment in a privately held company	700		700
Prepaid income tax	—		4,377
Long-term deposits	4,246		1,608
Other	361		216
	$	52,830	$	19,865

Accrued liabilities:



	March 31, 2018		June 30, 2017
	(in thousands)
Accrued compensation and benefits	$	13,878	$	13,727
Warranty accrual	611		1,866
Stock rotation accrual	1,774		1,871
Accrued professional fees	1,903		2,500
Accrued inventory	703		410
Accrued facilities related expenses	1,824		1,501
Accrued property, plant and equipment	33,755		2,241
Other accrued expenses	7,169		4,270
	$	61,617	$	28,386

The activities in the warranty accrual, included in accrued liabilities, are as follows



	Nine Months Ended March 31,
	2018				2017
	(in thousands)
Beginning balance	$	1,866			$	1,495
Additions (Reductions)	(1,203		)	*	898
Utilization	(52		)		(521		)
Ending balance	$	611			$	1,872

* Released a specific warranty reserve of approximately $1.0 million as the warranty period had expired.

The activities in the stock rotation accrual, included in accrued liabilities, are as follows:



	Nine Months Ended March 31,
	2018			2017
	(in thousands)
Beginning balance	$	1,871		$	1,988
Additions	2,147			3,986
Utilization	(2,244		)	(4,262		)
Ending balance	$	1,774		$	1,712

Debt Debt	9 Months Ended
Debt Debt	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt	Debt On August 15, 2017, the Company's Oregon subsidiary, Jireh Semiconductor Incorporated (“Jireh”), entered into a credit agreement with a financial institution (the “Bank”) that provided a term loan in an amount up to $30.0 million for the purpose of purchasing certain equipment for our fabrication facility located in Oregon. The obligation under the credit agreement is secured by substantially all assets of Jireh and guaranteed by the Company. The credit agreement has a five-year term and matures on August 15, 2022. On January 12, 2018, Jireh drew down the loan in the amount of $13.2 million. Beginning in September 2018, Jireh is required to pay to the Bank on each payment date, the outstanding principal amount of the loan in monthly installments. The loan accrues interest based on an adjusted London Interbank Offered Rate ("LIBOR") as defined in the credit agreement, plus specified applicable margin in the range of 1.75% to 2.25%, based on the outstanding balance of the loan. The credit agreement contains customary restrictive covenants and includes certain financial covenants that require the Company to maintain, on a consolidated basis, specified financial ratios and fixed charge coverage ratio. The Company is in compliance with these covenants. As of March 31, 2018, the outstanding balances of the term loan were $13.2 million.

Joint Venture

9 Months Ended

Mar. 31, 2018

Equity Method Investments and Joint Ventures [Abstract]

Joint Venture

On March 29, 2016, the Company entered into a joint venture contract (the “JV Agreement”) with two investment funds owned by the Municipality of Chongqing (the “Chongqing Funds”), pursuant to which the Company and the Chongqing Funds formed a joint venture, (the “JV Company”), for the purpose of constructing and operating a power semiconductor packaging, testing and 12-inch wafer fabrication facility in the Liangjiang New Area of Chongqing, China (the “JV Transaction”). The total initial capitalization of the JV Company is $330.0 million (the “Initial Capitalization”), which includes cash contribution from the Chongqing Funds and contributions of cash, equipment and intangible assets from the Company. The Initial Capitalization is expected to be completed in stages. As of March 31, 2018, the Chongqing Funds contributed approximately $162.0 million of initial capital in cash, including $42.0 million of contribution in March 2018. The Company owns 51%, and the Chongqing Funds own 49%, of the equity interest in the JV Company. If both parties agree that the termination of the JV Company is in the best interest of each party or the JV Company is bankrupt or insolvent where either party may terminate early, after paying the debts of the JV Company, the remaining assets of the JV Company shall be paid to the Chongqing Funds to cover the principal of its total paid-in contributions plus interest at 10% simple annual rate prior to distributing the balance of the JV Company's assets to the Company. The JV Company is in the pre-production phase and the Company expects the JV Company to complete its assembly and testing facilities in the quarter ending June 30, 2018 and fabrication facilities in December 2018.

There is no private land ownership in China. Individuals and companies are permitted to acquire land use rights for specific purpose. In September 2016, the JV Company paid approximately $8.7 million for land use rights to build the manufacturing facility. In March 2017, the JV Company received the necessary land use right certificate from the PRC government. The land use rights will expire on November 30, 2066.

As part of the JV Transaction, the JV Company entered into an Engineering, Procurement and Construction Contract (the “EPC Contract”) with The IT Electronics Eleventh Design & Research Institute Scientific and Technological Engineering Corporation Limited (the “Contractor”), effective as of January 10, 2017 (the "Effective Date"), pursuant which the Contractor was engaged to construct the manufacturing facility contemplated under the JV Agreement. Under the EPC Contract, the Contractor’s obligations include, but are not limited to: (i) the development of conceptual design, initial design, construction drawing design and optimization, and submission of such designs to the JV Company for examination and confirmation; and (ii) the construction of the assembly and wafer fabrication facilities and related procurement services, including the selection and engagement of subcontractors, in accordance with a construction schedule agreed upon by the parties. The total price payable under the EPC Contract is Chinese Renminbi (RMB) 540.0 million, or approximately $78.0 million based on the currency exchange rate between RMB and U.S. Dollars on the Effective Date, which consists of $2.8 million (RMB 19.5 million) of design fees (“Design Fees”) and $75.2 million (RMB 520.5 million) of construction and procurement fees (including compliance with safety and aesthetic requirements) (“Construction Fees”). The payment is subject to volatility as a result of exposure to fluctuations in RMB foreign exchange rates. The Design Fees and Construction Fees are paid by the JV Company pursuant to a payment schedule based on the progress of the construction and the achievements of specified milestones. As of March 31, 2018, the JV Company paid approximately $57.0 million (RMB 358.9 million), and expects to pay the remaining of $28.8 million (RMB 181.1 million) in calendar year 2018.

The changes in total stockholders' equity and noncontrolling interest were as follows (in thousands):



	Total AOS Stockholders' Equity			Noncontrolling Interest			Total Equity
Balance, June 30, 2017	$	270,770		$	27,779		$	298,549
Exercise of common stock options and release of RSUs	1,352			—			1,352
Reissuance of treasury stock upon exercise of common stock options and release of RSUs	(91		)	—			(91		)
Withholding tax on restricted stock units	(2,248		)	—			(2,248		)
Issuance of shares under ESPP	1,439			—			1,439
Repurchase of common shares under shares repurchase program	(12,016		)	—			(12,016		)
Stock-based compensation expense	8,477			—			8,477
Net income (loss)	13,242			(5,269		)	7,973
Deferred tax asset related to ASU 2016-16 adoption	(5,480		)	—			(5,480		)
Cumulative translation adjustment	4,848			4,398			9,246
Contributions from noncontrolling interest	—			128,994			128,994
Balance, March 31, 2018	$	280,293		$	155,902		$	436,195

Shareholders' Equity and Share-based Compensation

9 Months Ended

Mar. 31, 2018

Share-based Compensation [Abstract]

Shareholders' Equity and Share-based Compensation

Share Repurchase

In September 2017, the Board of Directors terminated the repurchase program that was previously approved in 2015 and approved a new repurchase program (the “Repurchase Program”), which allows the Company to repurchase its common shares from the open market pursuant to a pre-established Rule 10b5-1 trading plan or through privately negotiated transactions up to an aggregate of $30.0 million. The amount and timing of any repurchases under the Repurchase Program depend on a number of factors, including but not limited to, the trading price, volume and availability of the Company's common shares. Shares repurchased under this program are accounted for as treasury shares and the total cost of shares repurchased is recorded as a reduction of shareholders' equity.

During the nine months ended March 31, 2018, the Company repurchased an aggregate of 748,936 shares from the open market, for a total cost of $12.0 million, at an average price of $16.01 per share. Since the inception of the prior repurchase program in 2010, the Company repurchased an aggregate of 6,472,029 shares from the open market including shares purchased in a dutch tender offer for a total cost of $62.8 million, at an average price of $9.70 per share, excluding fees and related expenses. No repurchased shares have been retired. Of the 6,472,029 repurchased shares, 132,353 shares with a weighted average repurchase price of $10.50 per share, were reissued at an average price of $5.83 per share pursuant to option exercises and vested restricted share units. As of March 31, 2018, approximately $18.0 million remained available under the Repurchase Program.

Stock Options

The Company did not grant any stock options during the nine months ended March 31, 2018. The number of options expected to vest is the result of applying the pre-vesting forfeiture rate assumption to total outstanding options.

The following table summarizes the Company's stock option activities for the nine months ended March 31, 2018:



					Weighted
			Weighted		Average
			Average		Remaining
	Number of		Exercise Price		Contractual	Aggregate
	Shares		Per Share		Term (in years)	Intrinsic Value
Outstanding at June 30, 2017	1,053,367		$	10.98	4.43	$	6,212,660
Exercised	(133,514	)	$	10.90		$	818,624
Outstanding at March 31, 2018	919,853		$	10.99	4.19	$	4,521,710
Options vested and expected to vest	919,821		$	10.99	4.19	$	4,521,497
Exercisable at March 31, 2018	916,936		$	11.00	4.19	$	4,502,312

Restricted Stock Units ("RSUs")

The following table summarizes the Company's RSU activities for the nine months ended March 31, 2018:



	Number of Restricted Stock Units		Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Recognition Period (Years)	Aggregate Intrinsic Value
Nonvested at June 30, 2017	1,144,865		$	14.11	1.76	$	19,084,900
Granted	745,071		$	16.40
Vested	(473,657	)	$	13.58
Forfeited	(63,403	)	$	14.04
Nonvested at March 31, 2018	1,352,876		$	15.56	1.95	$	20,901,934
RSUs vested and expected to vest	1,177,238				1.87	$	18,188,334

The fair value of RSU is based on the market price of the Company's share on the date of grant.

In March 2017 and 2018, the Company granted 170,000 and 298,000 performance-based RSUs (“PRSUs”) to its certain personnel. The number shares to be issued under the PRSU are determined based on the level of attainment of predetermined financial goals. The PRSU vests in four equal annual installments from the first anniversary date after the grant date if certain predetermined financial goals were met. The Company recorded approximately $0.4 million and $1.1 million of expenses for these PRSUs during the three and nine months ended March 31, 2018, and approximately $68,000 of such expenses in the three and nine months ended March 31, 2017.

The Board previously approved the incentive cash bonus plan (the “Plan”) for the calendar year commencing January 1, 2017 pursuant to which each executive officer of the Company who continues in service through the end of the calendar year would be eligible to receive an incentive award, payable solely in cash, based on the level of attainment of certain specified Company performance goals. On November 15, 2017, the Board approved an amendment to the Plan that permits the Company to pay up to 50% of such incentive awards in common shares of the Company. The Company recorded $1.3 million of such RSUs expenses during the nine months ended March 31, 2018.

Employee Share Purchase Plan ("ESPP")

The assumptions used to estimate the fair values of common shares issued under the ESPP were as follows:




	Nine Months Ended March 31,
	2018
Volatility rate	45.32%
Risk-free interest rate	1.4% - 1.7%
Expected term	1.3 years
Dividend yield	0%

Share-based Compensation Expense

The total share-based compensation expense related to stock options, RSUs and ESPP described above, recognized in the condensed consolidated statements of operations for the periods presented was as follows:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Cost of goods sold	$	449	$	222	$	1,180	$	622
Research and development	361		395		1,340		1,138
Selling, general and administrative	1,650		1,098		5,957		2,825
	$	2,460	$	1,715	$	8,477	$	4,585

As of March 31, 2018, total unrecognized compensation cost under the Company's equity plans was $15.6 million, which is expected to be recognized over a weighted-average period of 1.8 years.

Income Taxes	9 Months Ended
Income Taxes	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the three months ended March 31, 2018, the Company recognized income tax expense of approximately $0.8 million, which included a discrete tax benefit of $0.2 million related principally to prior year tax reserve releases. For the three months ended March 31, 2017, the Company recognized income tax expense of approximately $0.5 million, which included a discrete tax benefit of $0.6 million related principally to prior year tax reserve releases. Excluding the discrete income tax items, the estimated effective tax rate for the three months ended March 31, 2018 was 291.8% compared to 38.8% for the three months ended March 31, 2017. The changes in the effective tax rate and tax expense between the periods resulted primarily from the reduction in the U.S. corporate tax rate following the enactment of the 2017 U.S. Tax Cut and Jobs Act along with changes in the mix of earnings in various geographic jurisdictions between the current year and the same period of last year. For the nine months ended March 31, 2018, the Company recognized an income tax expense of approximately $0.03 million, which included a discrete tax benefit of $2.7 million related to remeasuring the Company’s U.S. deferred tax assets and liabilities following enactment of the 2017 U.S. Tax Cut and Jobs Act in December 2017 and a discrete tax benefit of $0.2 million related principally to prior year tax reserve releases. For the nine months ended March 31, 2017, the Company recognized income tax expense of approximately $2.8 million, which included a discrete tax benefit of $0.6 million related principally to prior year tax reserve releases. Excluding the discrete income tax items, the estimated effective tax rate for the nine months ended March 31, 2018 was 35.5% compared to 36.6% for the nine months ended March 31, 2017. The changes in the effective tax rate and tax expense between the periods resulted primarily from the reduction in the U.S. corporate tax rate following the enactment of the 2017 U.S. Tax Cut and Jobs Act along with changes in the mix of earnings in various geographic jurisdictions between the current year and the same period of last year. During the quarter ended September 30, 2016, the Company contributed certain packaging equipment as required by the JV Agreement by transferring the legal titles of such equipment to the JV Company. As a result of the transfer, the Company reduced its deferred tax assets by $6.6 million and recorded a $6.6 million in prepaid tax asset, which was amortized to tax expense over the useful life of the assets. As of June 30, 2017, the prepaid tax asset was amortized down to $5.5 million, of which $1.1 million and $4.4 million were included in prepaid and other current assets and other long-term assets on the Company's balance sheet, respectively. On July 1, 2017, the Company adopted ASU 2016-16, Intra-Entity Transfers of Assets other than Inventory, which resulted in a de-recognition of a prepaid tax asset of $5.5 million related to the prior period intra-entity asset transfer with the JV Company, with an offsetting reduction to retained earnings. Because the JV Company has a full valuation allowance, there was no change to the Company’s net deferred tax assets. The Company files its income tax returns in the United States and in various foreign jurisdictions. The tax years 2002 to 2017 remain open to examination by U.S. federal and state tax authorities. The tax years 2010 to 2017 remain open to examination by foreign tax authorities. The Company's income tax returns are subject to examinations by the Internal Revenue Service and other tax authorities in various jurisdictions. In accordance with the guidance on the accounting for uncertainty in income taxes, the Company regularly assesses the likelihood of adverse outcomes resulting from these examinations to determine the adequacy of its provision for income taxes. These assessments can require considerable estimates and judgments. As of March 31, 2018, the gross amount of unrecognized tax benefits was approximately $6.7 million, of which $4.0 million, if recognized, would reduce the effective income tax rate in future periods. If the Company's estimate of income tax liabilities proves to be less than the ultimate assessment, then a further charge to expense would be required. If events occur and the payment of these amounts ultimately proves to be unnecessary, the reversal of the liabilities would result in tax benefits being recognized in the period when the Company determines the liabilities are no longer necessary. The Company does not anticipate any material changes to its uncertain tax positions during the next twelve months. On July 27, 2015, in Altera Corp. v. Commissioner, the U.S. Tax Court issued an opinion related to the treatment of share-based compensation expense in an intercompany cost-sharing arrangement. A final decision has yet to be issued by the Tax Court due to other outstanding issues related to the case. At this time, the U.S. Department of the Treasury has not withdrawn the requirement to include share-based compensation from its regulations. Due to the uncertainty surrounding the status of the current regulations, questions related to the scope of potential benefits, and the risk of the Tax Court’s decision being overturned upon appeal, the Company has not recorded any benefit as of March 31, 2018. The Company will continue to monitor ongoing developments and potential impacts to its financial statements.

Segment and Geographic Information

9 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Segment and Geographic Information

The Company is organized as, and operates in, one operating segment: the design, development and supply of power semiconductor products for computing, consumer electronics, communication and industrial applications. The chief operating decision-maker is the Chief Executive Officer. The financial information presented to the Company's Chief Executive Officer is on a consolidated basis, accompanied by information about revenue by customer and geographic region, for purposes of evaluating financial performance and allocating resources. The Company has one business segment, and there are no segment managers who are held accountable for operations, operating results and plans for products or components below the consolidated unit level. Accordingly, the Company reports as a single operating segment.

The Company sells its products primarily to distributors in the Asia Pacific region, who in turn sell these products to end customers. Because the Company's distributors sell their products to end customers which may have a global presence, revenue by geographical location is not necessarily representative of the geographical distribution of sales to end user markets.

The revenue by geographical location in the following tables is based on the country or region to which the products were shipped:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Hong Kong	$	84,632	$	75,785	$	252,302	$	236,873
China	15,849		15,334		52,122		42,159
South Korea	243		294		831		1,053
United States	1,358		1,075		4,050		2,767
Other countries	820		793		2,351		2,478
	$	102,902	$	93,281	$	311,656	$	285,330

The following is a summary of revenue by product type:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Power discrete	$	83,982	$	70,794	$	252,754	$	212,044
Power IC	15,685		19,309		49,540		64,166
Packaging and testing services	3,235		3,178		9,362		9,120
	$	102,902	$	93,281	$	311,656	$	285,330

Long-lived assets, net consisting of property, plant and equipment and land use rights, by geographical area are as follows:



	March 31, 2018		June 30, 2017
	(in thousands)
China	$	176,433	$	85,691
United States	81,675		61,787
Other Countries	687		713
	$	258,795	$	148,191

Commitments and Contingencies

9 Months Ended

Mar. 31, 2018

Commitments and Contingencies Disclosure [Abstract]

Commitments and Contingencies

Purchase Commitments

As of March 31, 2018 and June 30, 2017, the Company had approximately $38.4 million and $25.7 million, respectively, of outstanding purchase commitments primarily for purchases of semiconductor raw materials, wafers, spare parts and packaging and testing services, and approximately $89.6 million and $69.2 million, respectively, of capital commitments for the purchase of property and equipment and EPC construction.

Operating Lease Obligations

Except as set forth below, there have been no material changes to the operating lease obligations the Company previously disclosed in its Annual Report on Form 10-K for the year ended June 30, 2017, filed with the SEC on September 5, 2017.

In April 2018, the Company signed an approximately 5,000 square footage office lease for its research and design function, which is located in Austin, Texas. This non-cancelable operating lease term is 76 months with its estimated commencement date as July 2018. Future minimum lease payments of the lease at March 31, 2018 are as follows:



Year ending June 30,	Operating Leases
	(in thousands)
2019	$	96
2020	127
2021	131
2022	135
2023	139
Thereafter	192
	$	820

Other Commitments

See Note 4, Note 5 and Note 6 of the Notes to the Condensed Consolidated Financial Statements contained in this Quarterly Report on Form 10-Q for descriptions of commitments including STMicro license, debt and Joint Venture.

Contingencies and Indemnities

The Company is currently not a party to any pending material legal proceedings. The Company has in the past, and may from time to time in the future, become involved in legal proceedings arising from the normal course of business activities. The semiconductor industry is characterized by frequent claims and litigation, including claims regarding patent and other intellectual property rights as well as improper hiring practices. Irrespective of the validity of such claims, the Company could incur significant costs in the defense of such claims and suffer adverse effects on its operations.

The Company is a party to a variety of agreements that it has contracted with various third parties. Pursuant to these agreements, the Company may be obligated to indemnify another party to such an agreement with respect to certain matters. Typically, these obligations arise in the context of contracts entered into by the Company, under which the Company customarily agrees to hold the other party harmless against losses arising from a breach of representations and covenants related to such matters as title to assets sold, certain intellectual property rights, specified environmental matters and certain income taxes. In these circumstances, payment by the Company is customarily conditioned on the other party making a claim pursuant to the procedures specified in the particular contract, which procedures typically allow the Company to challenge the other party's claim. Further, the Company's obligations under these agreements may be limited in time and/or amount, and in some instances, the Company may have recourse against third parties for certain payments made by it under these agreements. The Company has not historically paid or recorded any material indemnifications and no accrual has been made at March 31, 2018 and June 30, 2017.

The Company has agreed to indemnify its directors and certain employees as permitted by law and pursuant to its Bye-laws, and has entered into indemnification agreements with its directors and executive officers. The Company has not recorded a liability associated with these indemnification arrangements, as it historically has not incurred any material costs associated with such indemnification obligations. Costs associated with such indemnification obligations may be mitigated by insurance coverage that the Company maintains. However, such insurance may not cover any, or may cover only a portion of, the amounts the Company may be required to pay. In addition, the Company may not be able to maintain such insurance coverage in the future.

Subsequent Events	9 Months Ended
Subsequent Events	Mar. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On May 1, 2018, the Company's Oregon subsidiary, Jireh Semiconductor Incorporated (“Jireh”), entered into a credit agreement with a financial institution (the “Bank”) that provided a term loan in an amount of $17.8 million. The obligation under the credit agreement is secured by certain assets of Jireh and guaranteed by the Company. The loan accrues interest based on a fixed rate of 5.04% based on the outstanding balance of the loan. The credit agreement contains customary restrictive covenants and includes certain financial covenants that require the Company to maintain, on a consolidated basis, specified financial ratios.

The Company and Significant Accounting Policies (Policies)	9 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Preparation	Basis of Preparation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (“U.S. GAAP”) for interim financial information and with the instructions to Article 10 of Securities and Exchange Commission Regulation S-X, as amended. They do not include all information and footnotes necessary for a fair presentation of financial position, results of operations and cash flows in conformity with U.S. GAAP for complete financial statements. These condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Company’s Annual Report on Form 10-K for the fiscal year ended June 30, 2017. All significant intercompany balances and transactions have been eliminated in consolidation. In the opinion of management, all adjustments (consisting of normal recurring adjustments and accruals) considered necessary for a fair presentation of the results of operations for the periods presented have been included in the interim periods. Operating results for the nine months ended March 31, 2018 are not necessarily indicative of the results that may be expected for the fiscal year ending June 30, 2018. The condensed consolidated balance sheet at June 30, 2017 is derived from the audited financial statements included in the Company’s Annual Report on Form 10-K for the fiscal year ended June 30, 2017.
Use of Estimates	Use of Estimates The preparation of the condensed consolidated financial statements in conformity with U.S. GAAP requires the Company to make estimates, judgments and assumptions that affect the reported amounts of assets, liabilities, revenue and expenses. To the extent there are material differences between these estimates and actual results, the Company's condensed consolidated financial statements will be affected. On an ongoing basis, the Company evaluates the estimates, judgments and assumptions including those related to stock rotation returns, price adjustments, allowance for doubtful accounts, inventory reserves, warranty accrual, income taxes, share-based compensation, and useful lives for property, plant and equipment and intangible assets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The fair values of cash equivalents are based on observable market prices and have been categorized in Level 1 in the fair value hierarchy. Cash equivalents consist primarily of short term bank deposits. The carrying values of financial instruments such as cash and cash equivalents, accounts receivable and accounts payable approximate their carrying values due to their short-term maturities.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. The Company's accumulated other comprehensive income (loss) consists of cumulative foreign currency translation adjustments. Total comprehensive income (loss) is presented in the condensed consolidated statements of comprehensive income (loss).
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2017, the FASB issued ASU 2017-09, "Compensation -Stock Compensation: Scope of Modification Accounting ("ASU 2017-09"). ASU 2017-09 is an update to the existing guidance to clarify when modification accounting would be applied for a change to the terms or conditions of a share-based award. Under this new guidance, modification accounting is required only if the fair value, a vesting condition, or the classification of the award changes as a result of the change in terms or conditions. This ASU will be effective for annual periods, and interim periods within those annual periods, beginning after December 15, 2017 with early adoption permitted. The Company does not regularly modify the terms and conditions of its share-based awards and does not expect the adoption of this guidance to have a significant impact on its financial statements. In November 2016, the FASB issued ASU 2016-18, "Statement of Cash Flows: Restricted Cash ("ASU 2016-18"). ASU 2016-18 requires amounts generally described as restricted cash and restricted cash equivalents be included with cash and cash equivalents when reconciling the total beginning and ending amounts for the periods shown on the statement of cash flows. This ASU will be effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted and requires retrospective adoption. The Company does not expect the adoption of this guidance will have a material impact on its consolidated financial position, results of operations or cash flows. In August 2016, the FASB issued ASU No. 2016-15, "Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments ("ASU 2016-15"). ASU 2016-15 identifies how certain cash receipts and cash payments are presented and classified in the Statement of Cash Flows under Topic 230. ASU 2016-15 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. Upon adoption, entities must apply the guidance retrospectively to all periods presented. The Company is currently evaluating the impact the adoption of ASU 2016-15 will have on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases. This guidance requires a dual approach for lessee accounting under which a lessee will account for leases as finance leases or operating leases. Both finance and operating leases will result in the lessee recognizing a right-of-use asset and a corresponding liability on its balance sheet, with differing methodology for income statement recognition. This guidance is effective for public business entities for fiscal years, and interim periods within those years, beginning after December 15, 2018, and early adoption is permitted. A modified retrospective approach is required for all leases existing or entered into after the beginning of the earliest comparative period in the consolidated financial statements. The Company is currently assessing the impact that adoption of this guidance will have on its consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (ASC 606). The standard provides companies with a single model for use in accounting for revenue arising from contracts with customers and supersedes current revenue recognition guidance, including industry-specific revenue guidance. The core principle of the model is to recognize revenue when control of the goods or services transfers to the customer, as opposed to recognizing revenue when the risks and rewards transfer to the customer under the existing revenue guidance. The Company will adopt the new revenue standard on July 1, 2018 utilizing the modified retrospective method. Upon adoption on July 1, 2018, the Company will record a cumulative effect to retained earnings related to deferred revenue balance due to the change in revenue recognition for its two U.S.-based distributors as discussed below. The Company does not expect the cumulative effect adjustment to have a material impact on its consolidated financial statements. The amount as previously disclosed in our annual financial statements was a net amount of $0.8 million as of June 30, 2017 and the Company does not expect the balance as of June 30, 2018 to be materially different. The Company is in the process of finalizing its assessment and implemented policies, processes, and controls to support the standard measurement and disclosure requirements. Under ASC 606, the Company's product sales consist of a single performance obligation that is satisfied at a point in time. The Company recognizes product revenue from distributors and other customers when the products are shipped or delivered to the customers based on the terms of the purchase orders and sales agreements, primarily because the distributors and customers have legal title and physical possession of the product; can direct the use of the product; are obligated to pay the Company for the product; and bear significant risks and rewards of ownership of the products. The change for the Company under ASC 606 relates to the timing of revenue recognition with two U.S.-based distributors. Sales to these distributors are governed under the terms of agreements providing extended price protection and other return rights. Under current accounting standards, revenue and costs related to these sales are deferred until distributors sold to the end customers and the amount of price adjustments is fixed and finalized. Under ASC 606, the transaction price takes into consideration the effect of variable consideration such as price adjustments and returns rights, which are estimated and recorded at the time the goods are delivered. Accordingly, the Company will recognize revenue at the time of shipment or delivery to these two distributors, adjusted for estimates of the price adjustments and product returns based on historical data and other available information. Revenue from other non-U.S. distributors and direct customers, which consists of majority of the Company's total revenue, is currently recognized at the time of shipment or delivery to the distributors and direct customers, Accordingly, revenue recognition with these distributors and direct customers remains unchanged upon adoption of ASC 606.
Concentration of Credit Risk	The Company manages its credit risk associated with exposure to distributors and direct customers on outstanding accounts receivable through the application and review of credit approvals, credit ratings and other monitoring procedures. In some instances, the Company also obtains letters of credit from certain customers. Credit sales, which are mainly on credit terms of 30 to 60 days, are only made to customers who meet the Company's credit requirements, while sales to new customers or customers with low credit ratings are usually made on an advance payment basis. The Company considers its trade accounts receivable to be of good credit quality because its key distributors and direct customers have long-standing business relationships with the Company and the Company has not experienced any significant write-offs of accounts receivable in the past. The Company closely monitors the aging of accounts receivable from its distributors and direct customers, and regularly reviews their financial positions, when available.

Net Income (Loss) Per Share (Tables)

9 Months Ended

Mar. 31, 2018

Earnings Per Share [Abstract]

Schedule of Earnings Per Share, Basic and Diluted

The following table presents the calculation of basic and diluted net income per share attributable to common shareholders:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands, except per share data)
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$	1,651	$	3,556	$	13,242	$	9,710

Denominator:
Basic:
Weighted average number of common shares used to compute basic net income per share	23,795		23,675		23,914		23,396
Diluted:
Weighted average number of common shares used to compute basic net income per share	23,795		23,675		23,914		23,396
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	960		1,276		1,002		1,385
Weighted average number of common shares used to compute diluted net income per share	24,755		24,951		24,916		24,781
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic	$	0.07	$	0.15	$	0.55	$	0.42
Diluted	$	0.07	$	0.14	$	0.53	$	0.39

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

The following potential dilutive securities were excluded from the computation of diluted net income per share as their effect would have been anti-dilutive:



	Three Months Ended March 31,		Nine Months Ended March 31,
	2018	2017	2018	2017
	(in thousands)		(in thousands)
Employee stock options and RSUs	165	3	167	83
ESPP	381	20	157	12
Total potential dilutive securities	546	23	324	95

Concentration of Credit Risk and Significant Customers (Tables)

9 Months Ended

Mar. 31, 2018

Risks and Uncertainties [Abstract]

Schedules of Concentration of Risk, by Risk Factor

Summarized below are individual customers whose revenue or accounts receivable balances were more than 10% of the respective total consolidated amounts:



	Three Months Ended March 31,				Nine Months Ended March 31,
Percentage of revenue	2018		2017		2018		2017
Customer A	25.9	%	27.3	%	28.1	%	26.2	%
Customer B	37.0	%	36.6	%	34.8	%	36.3	%
Customer C	*		10.5	%	*		11.7	%

* Less than 10%



	March 31, 2018		June 30, 2017
Percentage of accounts receivable	March 31, 2018		June 30, 2017
Customer A	19.9	%	33.2	%
Customer B	29.3	%	13.2	%
Customer C	11.9	%	16.4	%

Balance Sheet Components (Tables)

9 Months Ended

Mar. 31, 2018

Balance Sheet Related Disclosures [Abstract]

Schedule of Accounts, Notes, Loans and Financing Receivable

Accounts receivable, net:



	March 31, 2018			June 30, 2017
	(in thousands)
Accounts receivable	$	49,607		$	48,039
Less: Allowance for price adjustments	(20,650		)	(19,599		)
Less: Allowance for doubtful accounts	(30		)	(30		)
Accounts receivable, net	$	28,927		$	28,410

Schedule of Inventory, Current

Inventories:



	March 31, 2018		June 30, 2017
	(in thousands)
Raw materials	$	45,295	$	32,118
Work in-process	36,252		36,081
Finished goods	8,925		8,055
	$	90,472	$	76,254

Other Current Assets

Other current assets:



	March 31, 2018		June 30, 2017
	(in thousands)
VAT receivable	$	12,979	$	591
Other prepaid expenses	2,438		2,171
Prepayment to supplier	611		148
Prepaid income tax	536		1,356
Other receivable	551		617
	$	17,115	$	4,883

Property, Plant and Equipment

operty, plant and equipment, net:



	March 31, 2018			June 30, 2017
	(in thousands)
Land	$	4,877		$	4,877
Building	4,325			4,325
Manufacturing machinery and equipment	250,341			215,275
Equipment and tooling	15,098			13,549
Computer equipment and software	25,310			24,346
Office furniture and equipment	2,150			1,935
Leasehold improvements	29,740			29,136
Land use rights	9,566			8,849
	341,407			302,292
Less: accumulated depreciation	(222,568		)	(194,882		)
	118,839			107,410
Equipment and construction in progress	139,956			40,781
Property, plant and equipment, net	$	258,795		$	148,191

Intangible Assets Disclosure

Intangible assets, net:



	March 31, 2018			June 30, 2017
	(in thousands)
License fees	$	17,633		$	1,248
Trade name	268			268
Customer relationships	1,150			1,150
	19,051			2,666
Less: accumulated amortization	(2,701		)	(2,653		)
	16,350			13
Goodwill	269			269
Intangible assets, net	$	16,619		$	282

Schedule of Other Assets, Noncurrent

Other long-term assets:



	March 31, 2018		June 30, 2017
	(in thousands)
Prepayments for property and equipment	$	47,523	$	12,964
Investment in a privately held company	700		700
Prepaid income tax	—		4,377
Long-term deposits	4,246		1,608
Other	361		216
	$	52,830	$	19,865

Schedule of Accrued Liabilities

Accrued liabilities:



	March 31, 2018		June 30, 2017
	(in thousands)
Accrued compensation and benefits	$	13,878	$	13,727
Warranty accrual	611		1,866
Stock rotation accrual	1,774		1,871
Accrued professional fees	1,903		2,500
Accrued inventory	703		410
Accrued facilities related expenses	1,824		1,501
Accrued property, plant and equipment	33,755		2,241
Other accrued expenses	7,169		4,270
	$	61,617	$	28,386

Schedule of Product Warranty Liability

The activities in the warranty accrual, included in accrued liabilities, are as follows



	Nine Months Ended March 31,
	2018				2017
	(in thousands)
Beginning balance	$	1,866			$	1,495
Additions (Reductions)	(1,203		)	*	898
Utilization	(52		)		(521		)
Ending balance	$	611			$	1,872

* Released a specific warranty reserve of approximately $1.0 million as the warranty period had expired.

Stock Rotation Accrual

The activities in the stock rotation accrual, included in accrued liabilities, are as follows:



	Nine Months Ended March 31,
	2018			2017
	(in thousands)
Beginning balance	$	1,871		$	1,988
Additions	2,147			3,986
Utilization	(2,244		)	(4,262		)
Ending balance	$	1,774		$	1,712

Joint Venture (Tables)

9 Months Ended

Mar. 31, 2018

Equity Method Investments and Joint Ventures [Abstract]

Schedule of Stockholders Equity

The changes in total stockholders' equity and noncontrolling interest were as follows (in thousands):



	Total AOS Stockholders' Equity			Noncontrolling Interest			Total Equity
Balance, June 30, 2017	$	270,770		$	27,779		$	298,549
Exercise of common stock options and release of RSUs	1,352			—			1,352
Reissuance of treasury stock upon exercise of common stock options and release of RSUs	(91		)	—			(91		)
Withholding tax on restricted stock units	(2,248		)	—			(2,248		)
Issuance of shares under ESPP	1,439			—			1,439
Repurchase of common shares under shares repurchase program	(12,016		)	—			(12,016		)
Stock-based compensation expense	8,477			—			8,477
Net income (loss)	13,242			(5,269		)	7,973
Deferred tax asset related to ASU 2016-16 adoption	(5,480		)	—			(5,480		)
Cumulative translation adjustment	4,848			4,398			9,246
Contributions from noncontrolling interest	—			128,994			128,994
Balance, March 31, 2018	$	280,293		$	155,902		$	436,195

Shareholders' Equity and Share-based Compensation (Tables)

9 Months Ended

Mar. 31, 2018

Share-based Compensation [Abstract]

Summary of Stock Option Activities

Stock Options

The Company did not grant any stock options during the nine months ended March 31, 2018. The number of options expected to vest is the result of applying the pre-vesting forfeiture rate assumption to total outstanding options.

The following table summarizes the Company's stock option activities for the nine months ended March 31, 2018:



					Weighted
			Weighted		Average
			Average		Remaining
	Number of		Exercise Price		Contractual	Aggregate
	Shares		Per Share		Term (in years)	Intrinsic Value
Outstanding at June 30, 2017	1,053,367		$	10.98	4.43	$	6,212,660
Exercised	(133,514	)	$	10.90		$	818,624
Outstanding at March 31, 2018	919,853		$	10.99	4.19	$	4,521,710
Options vested and expected to vest	919,821		$	10.99	4.19	$	4,521,497
Exercisable at March 31, 2018	916,936		$	11.00	4.19	$	4,502,312

Restricted Stock Units Activity

Restricted Stock Units ("RSUs")

The following table summarizes the Company's RSU activities for the nine months ended March 31, 2018:



	Number of Restricted Stock Units		Weighted Average Grant Date Fair Value Per Share		Weighted Average Remaining Recognition Period (Years)	Aggregate Intrinsic Value
Nonvested at June 30, 2017	1,144,865		$	14.11	1.76	$	19,084,900
Granted	745,071		$	16.40
Vested	(473,657	)	$	13.58
Forfeited	(63,403	)	$	14.04
Nonvested at March 31, 2018	1,352,876		$	15.56	1.95	$	20,901,934
RSUs vested and expected to vest	1,177,238				1.87	$	18,188,334

The fair value of RSU is based on the market price of the Company's share on the date of grant.

Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions [Table Text Block]

Employee Share Purchase Plan ("ESPP")

The assumptions used to estimate the fair values of common shares issued under the ESPP were as follows:




	Nine Months Ended March 31,
	2018
Volatility rate	45.32%
Risk-free interest rate	1.4% - 1.7%
Expected term	1.3 years
Dividend yield	0%

Share-based Compensation, Allocation of Recognized Period Costs

Share-based Compensation Expense

The total share-based compensation expense related to stock options, RSUs and ESPP described above, recognized in the condensed consolidated statements of operations for the periods presented was as follows:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Cost of goods sold	$	449	$	222	$	1,180	$	622
Research and development	361		395		1,340		1,138
Selling, general and administrative	1,650		1,098		5,957		2,825
	$	2,460	$	1,715	$	8,477	$	4,585

Segment and Geographic Information (Tables)

9 Months Ended

Mar. 31, 2018

Segment Reporting [Abstract]

Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas

Long-lived assets, net consisting of property, plant and equipment and land use rights, by geographical area are as follows:



	March 31, 2018		June 30, 2017
	(in thousands)
China	$	176,433	$	85,691
United States	81,675		61,787
Other Countries	687		713
	$	258,795	$	148,191

The revenue by geographical location in the following tables is based on the country or region to which the products were shipped:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Hong Kong	$	84,632	$	75,785	$	252,302	$	236,873
China	15,849		15,334		52,122		42,159
South Korea	243		294		831		1,053
United States	1,358		1,075		4,050		2,767
Other countries	820		793		2,351		2,478
	$	102,902	$	93,281	$	311,656	$	285,330

Revenue from External Customers by Products and Services

The following is a summary of revenue by product type:



	Three Months Ended March 31,				Nine Months Ended March 31,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Power discrete	$	83,982	$	70,794	$	252,754	$	212,044
Power IC	15,685		19,309		49,540		64,166
Packaging and testing services	3,235		3,178		9,362		9,120
	$	102,902	$	93,281	$	311,656	$	285,330

The Company and Significant Accounting Policies Joint Venture (Details) - Facility in Liangjiang New Area of Chongqing (the 'Joint Venture') - USD ($) $ in Millions	1 Months Ended
	Mar. 31, 2016	Mar. 29, 2016
Parent Company
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	51.00%
Chongqing Funds
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	49.00%
Corporate Joint Venture
Initial capitalization of joint venture		$ 330.0

Net Income (Loss) Per Share - Basic and Diluted Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$ 1,651	$ 3,556	$ 13,242	$ 9,710
Basic:
Weighted average number of common shares used to compute basic net income per share	23,795	23,675	23,914	23,396
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	960	1,276	1,002	1,385
Weighted average number of common shares used to compute diluted net income per share	24,755	24,951	24,916	24,781
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic (in dollars per share)	$ 0.07	$ 0.15	$ 0.55	$ 0.42
Diluted (in dollars per share)	$ 0.07	$ 0.14	$ 0.53	$ 0.39

Net Income (Loss) Per Share - Potential Dilutive Shares (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	546	23	324	95
Employee stock options and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	165	3	167	83
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	381	20	157	12

Concentration of Credit Risk and Significant Customers - (Details)

3 Months Ended

9 Months Ended

Mar. 31, 2018

Jun. 30, 2017

Mar. 31, 2017

Mar. 31, 2018

Mar. 31, 2017

Minimum

Concentration Risk

Terms of credit sales, (in days)

30 days

Maximum

Concentration Risk

Terms of credit sales, (in days)

60 days

Customer A | Sales Revenue, Goods, Net | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

25.90%

27.30%

28.10%

26.20%

Customer A | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

19.90%

33.20%

Customer B | Sales Revenue, Goods, Net | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

37.00%

36.60%

34.80%

36.30%

Customer B | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

29.30%

13.20%

Customer C | Sales Revenue, Goods, Net | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

10.50%

^[1]

11.70%

Customer C | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

11.90%

16.40%

[1]	* Less than 10%

Balance Sheet Components - Accounts receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Accounts receivable	$ 49,607	$ 48,039
Less: Allowance for price adjustments	(20,650)	(19,599)
Less: Allowance for doubtful accounts	(30)	(30)
Accounts receivable, net	$ 28,927	$ 28,410

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Raw materials	$ 45,295	$ 32,118
Work in-process	36,252	36,081
Finished goods	8,925	8,055
Inventory, net	$ 90,472	$ 76,254

Balance Sheet Components - Other current assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
VAT receivable	$ 12,979	$ 591
Other prepaid expenses	2,438	2,171
Prepayment to supplier	611	148
Prepaid income tax	536	1,356
Other receivable	551	617
Other Assets, Current	$ 17,115	$ 4,883

Balance Sheet Components - Property, plant, and equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	$ 341,407	$ 302,292
Land Use Rights, Gross	9,566	8,849
Less: accumulated depreciation	(222,568)	(194,882)
Property, plant and equipment excluding equipment and construction in progress, net	118,839	107,410
Equipment and construction in progress	139,956	40,781
Property, plant and equipment, net	258,795	148,191
Land
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	4,877	4,877
Building
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	4,325	4,325
Manufacturing machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	250,341	215,275
Equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	15,098	13,549
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	25,310	24,346
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	2,150	1,935
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	$ 29,740	$ 29,136

Balance Sheet Components - Intangible assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	$ 19,051	$ 2,666
Less: accumulated amortization	(2,701)	(2,653)
Intangible Assets, Net (Excluding Goodwill)	16,350	13
Goodwill	269	269
Intangible assets, net	16,619	282
License fees
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	17,633	1,248
Trade name
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	268	268
Customer relationships
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	1,150	$ 1,150
STMicro \| License fees
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Net	$ 16,400

Balance Sheet Components - Intangible Assets, Additional Information (Details) - USD ($) $ in Thousands		9 Months Ended
	Sep. 05, 2017	Mar. 31, 2018	Mar. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Intangible Assets		$ 14,034	$ 0
STMicro \| License fees
Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Intangible Assets	$ 17,000	13,500
Payments to Acquire Intangible Assets in Calender Year 2017	10,100
Payments to Acquire Intangible Assets in Calender Year 2018	6,700
Payments to Acquire Intangible Assets in Calender Year 2019	$ 200
Finite-Lived Intangible Assets, Net		$ 16,400

Balance Sheet Components - Other long term assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Prepayments for property and equipment	$ 47,523	$ 12,964
Investment in a privately held company	700	700
Prepaid income tax	0	4,377
Long-term deposits	4,246	1,608
Other	361	216
Other long-term assets	$ 52,830	$ 19,865

Balance Sheet Components - Accrued liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016
Balance Sheet Related Disclosures [Abstract]
Accrued compensation and benefits	$ 13,878	$ 13,727
Warranty accrual	611	1,866	$ 1,872	$ 1,495
Stock rotation accrual	1,774	1,871	$ 1,712	$ 1,988
Accrued professional fees	1,903	2,500
Accrued inventory	703	410
Accrued facilities related expenses	1,824	1,501
Accrued Property, Plant and Equipment	33,755	2,241
Other accrued expenses	7,169	4,270
Accrued liabilities	$ 61,617	$ 28,386

Balance Sheet Components - Product Warranty Accrual (Details) - USD ($) $ in Thousands	9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Beginning balance	$ 1,866	$ 1,495
Additions (Reductions)	(1,203)	898
Utilization	(52)	(521)
Ending balance	611	$ 1,872
Release of specific warranty reserve	$ 1,000

Balance Sheet Components - Stock Rotation Accrual (Details) - USD ($) $ in Thousands	9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock Rotation Accrual Increae (Decrease) [Roll Forward]
Beginning balance	$ 1,871	$ 1,988
Additions	2,147	3,986
Utilization	(2,244)	(4,262)
Ending balance	$ 1,774	$ 1,712

Debt (Details) - Term Loan - Secured Debt - Variable Interest Rate Term Loan Maturing August 2022 - USD ($) $ in Millions	Aug. 15, 2017	Mar. 31, 2018	Jan. 12, 2018
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 30.0
Debt instrument, term	5 years
Amount outstanding		$ 13.2	$ 13.2
Minimum \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	1.75%
Maximum \| London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on variable rate	2.25%

Joint Venture - Narrative (Details) $ in Thousands	1 Months Ended			9 Months Ended		15 Months Ended		24 Months Ended
Joint Venture - Narrative (Details) $ in Thousands	Mar. 31, 2018 USD ($)	Sep. 30, 2016 USD ($)	Mar. 31, 2016	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2018 CNY (¥)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jan. 10, 2017 CNY (¥)	Jan. 10, 2017 USD ($)	Mar. 29, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Proceeds from investment by noncontrolling interest				$ 128,994	$ 33,000
Purchases of land use rights in JV Company				0	$ 8,737
Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Schedule of Equity Method Investments [Line Items]
Interest rate to concontrolling interest if joint venture is early terminated and liquidated			10.00%
Parent Company \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Schedule of Equity Method Investments [Line Items]
Percent ownership in joint venture			51.00%
Chongqing Funds \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Schedule of Equity Method Investments [Line Items]
Percent ownership in joint venture			49.00%
Corporate Joint Venture
Schedule of Equity Method Investments [Line Items]
Total price payable under EPC Contract										¥ 540,000,000	$ 78,000
Contractual Obligation, Payment						¥ 358,900,000	$ 57,000
Contract amount payable in calendar year 2018						¥ 181,100,000			$ 28,800
Corporate Joint Venture \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Schedule of Equity Method Investments [Line Items]
Initial capitalization of joint venture												$ 330,000
Purchases of land use rights in JV Company		$ 8,700
Corporate Joint Venture \| Design Fees
Schedule of Equity Method Investments [Line Items]
Total price payable under EPC Contract										19,500,000	2,800
Corporate Joint Venture \| Construction and Procurement Fees
Schedule of Equity Method Investments [Line Items]
Total price payable under EPC Contract										¥ 520,500,000	$ 75,200
Noncontrolling Interest
Schedule of Equity Method Investments [Line Items]
Proceeds from investment by noncontrolling interest	$ 42,000			$ 128,994				$ 162,000

Joint Venture - Changes in Total Stockholders' Equity (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		24 Months Ended	89 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2018
Schedule of Equity Method Investments [Line Items]
Balance, June 30, 2017				$ 298,549
Exercise of common stock options and release of RSUs				1,352
Reissuance of treasury stock upon exercise of common stock options and release of RSUs				(91)
Withholding tax on restricted stock units				(2,248)
Issuance of shares under ESPP				1,439
Repurchase of common shares under shares repurchase program				(12,016)			$ (62,800)
Stock-based compensation expense				8,477
Net income (loss)		$ (488)	$ 2,386	7,973	$ 6,473
Net loss attributable to noncontrolling interest		(2,139)	$ (1,170)	(5,269)	(3,237)
Cumulative translation adjustment				9,246
Contributions from noncontrolling interest				128,994	$ 33,000
Balance, March 31, 2018	$ 436,195	436,195		436,195		$ 436,195	436,195
Accounting Standards Update 2016-16
Schedule of Equity Method Investments [Line Items]
Deferred tax asset related to ASU 2016-16 adoption				(5,480)
Parent
Schedule of Equity Method Investments [Line Items]
Balance, June 30, 2017				270,770
Exercise of common stock options and release of RSUs				1,352
Reissuance of treasury stock upon exercise of common stock options and release of RSUs				(91)
Withholding tax on restricted stock units				(2,248)
Issuance of shares under ESPP				1,439
Repurchase of common shares under shares repurchase program				(12,016)
Stock-based compensation expense				8,477
Net income (loss)				13,242
Cumulative translation adjustment				4,848
Contributions from noncontrolling interest				0
Balance, March 31, 2018	280,293	280,293		280,293		280,293	280,293
Parent \| Accounting Standards Update 2016-16
Schedule of Equity Method Investments [Line Items]
Deferred tax asset related to ASU 2016-16 adoption				(5,480)
Noncontrolling Interest
Schedule of Equity Method Investments [Line Items]
Balance, June 30, 2017				27,779
Exercise of common stock options and release of RSUs				0
Reissuance of treasury stock upon exercise of common stock options and release of RSUs				0
Withholding tax on restricted stock units				0
Issuance of shares under ESPP				0
Repurchase of common shares under shares repurchase program				0
Stock-based compensation expense				0
Net loss attributable to noncontrolling interest				(5,269)
Cumulative translation adjustment				4,398
Contributions from noncontrolling interest	42,000			128,994		162,000
Balance, March 31, 2018	$ 155,902	$ 155,902		155,902		$ 155,902	$ 155,902
Noncontrolling Interest \| Accounting Standards Update 2016-16
Schedule of Equity Method Investments [Line Items]
Deferred tax asset related to ASU 2016-16 adoption				$ 0

Shareholders' Equity and Share-based Compensation - Shares Repurchase (Details) - USD ($)	3 Months Ended		9 Months Ended		89 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018
Class of Stock [Line Items]
Share repurchase program, authorized amount (USD in Millions)	$ 30,000,000		$ 30,000,000		$ 30,000,000
Shares Repurchase Program Remaining Balance	18,000,000		$ 18,000,000		$ 18,000,000
Repurchase of common shares under shares repurchase program			748,936		6,472,029
Repurchase of common shares under shares repurchase program			$ (12,016,000)		$ (62,800,000)
Treasury stock acquired, average price per share (in dollars per share)			$ 16.01		$ 9.70
Treasury Stock, Shares, Retired			0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross			0
Allocated share-based compensation expense	2,460,000	$ 1,715,000	$ 8,477,000	$ 4,585,000
Treasury Stock Reissued
Class of Stock [Line Items]
Treasury stock acquired, average price per share (in dollars per share)					$ 10.50
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures (in shares)					132,353
Treasury Stock Reissued, Average Price Per Share					$ 5.83
Performance Based Restricted Stock Units (PRSUs) Member [Member]
Class of Stock [Line Items]
Allocated share-based compensation expense	$ 400,000	$ 68,000	$ 1,100,000	$ 68,000

Shareholders' Equity and Share-based Compensation - Share-based Compensation (Details) - USD ($)	3 Months Ended			9 Months Ended	89 Months Ended
	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common shares under shares repurchase program				748,936	6,472,029
Options, Weighted-Average Remaining Contractual Life (in years)		4 years 5 months 5 days		4 years 2 months 9 days
Options vested and expected to vest, Number Outstanding (in shares)	919,821			919,821	919,821
Options vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 10.99			$ 10.99	$ 10.99
Options vested and expected to vest, Weighted Average Remaining Contractual Life (in years)				4 years 2 months 9 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 4,521,497			$ 4,521,497	$ 4,521,497
Options, Number Exercisable (in shares)	916,936			916,936	916,936
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 11.00			$ 11.00	$ 11.00
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	4 years 2 months 9 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 4,502,312			$ 4,502,312	$ 4,502,312
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at June 30, 2017				1,053,367
Granted (in shares)				0
Exercised (in shares)				(133,514)
Outstanding at March 31, 2018	919,853	1,053,367		919,853	919,853
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Outstanding at June 30, 2017 (in dollars per share)				$ 10.98
Exercised (in dollars per share)				10.90
Outstanding at December 31, 2017 (in dollars per share)	$ 10.99	$ 10.98		$ 10.99	$ 10.99
Options Outstanding Aggregate Intrinsic Value	$ 4,521,710	$ 6,212,660		$ 4,521,710	$ 4,521,710
Options Exercised Aggregate Intrinsic Value				$ 818,624
Performance Based Restricted Stock Units (PRSUs) Member [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted	298,000		170,000
Employee Share Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Volatility Rate				45.32%
Expected Term				1 year 3 months 18 days
Expected Dividend Rate				0.00%
Employee Share Purchase Plan [Member] \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk Free Interest Rate				1.40%
Employee Share Purchase Plan [Member] \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk Free Interest Rate				1.70%

Shareholders' Equity and Share-based Compensation - Stock Options Outstanding and Exercisable (Details) - $ / shares	3 Months Ended	9 Months Ended
	Jun. 30, 2017	Mar. 31, 2018
Share-based Compensation [Abstract]
Options, Number Outstanding (in shares)	1,053,367	919,853
Options, Weighted-Average Remaining Contractual Life (in years)	4 years 5 months 5 days	4 years 2 months 9 days
Options, Weighted-Average Exercise Price (in dollars per share)	$ 10.98	$ 10.99
Options, Number Exercisable (in shares)		916,936
Options, Weighted-Average Exercise Price (in dollars per share)		$ 11.00
Options vested and expected to vest, Number Outstanding (in shares)		919,821
Options vested and expected to vest, Weighted Average Remaining Contractual Life (in years)		4 years 2 months 9 days
Options vested and expected to vest, Weighted Average Exercise Price (in dollars per share)		$ 10.99

Shareholders' Equity and Share-based Compensation - Restricted Stock Activity (Details) - USD ($)	3 Months Ended			9 Months Ended
	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Weighted Average Remaining Recognition Period (Years)	1 year 9 months 18 days
Allocated share-based compensation expense	$ 2,460,000		$ 1,715,000	$ 8,477,000	$ 4,585,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested at June 30, 2017				1,144,865
Granted				745,071
Vested				(473,657)
Forfeited				(63,403)
Nonvested at March 31, 2018	1,352,876	1,144,865		1,352,876
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Nonvested at June 30, 2017				$ 14.11
Granted				16.40
Vested				13.58
Forfeited				14.04
Nonvested at March 31, 2018	$ 15.56	$ 14.11		$ 15.56
Weighted Average Remaining Recognition Period (Years)	1 year 11 months 12 days	1 year 9 months 4 days
RSUs Nonvested Aggregate Intrinsic Value	$ 20,901,934	$ 19,084,900		$ 20,901,934
RSUs vested and expected to vest, Outstanding (in shares)	1,177,238			1,177,238
RSUs vested and expected to vest, Weighted Average Remaining Recognition Period (in years)	1 year 10 months 13 days
RSUs vested and expected to vest, Aggregate Intrinsic Value	$ 18,188,334			$ 18,188,334
Performance Based Restricted Stock Units (PRSUs) Member [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Granted	298,000		170,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Allocated share-based compensation expense	$ 400,000		$ 68,000	$ 1,100,000	$ 68,000

Shareholders' Equity and Share-based Compensation - Share-based Compensation Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Nov. 15, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 2,460	$ 1,715	$ 8,477	$ 4,585
Unrecognized compensation expense	$ 15,600		15,600
Recognition period of share-based compensation expense (in years)	1 year 9 months 18 days
Cost of goods sold
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 449	222	1,180	622
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	361	395	1,340	1,138
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 1,650	$ 1,098	5,957	$ 2,825
Restricted Stock Units (RSUs) \| Incentive Cash Bonus Plan (The Plan)
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense			$ 1,300
Incentive award payable in shares, percent of total award (up to 50%)					50.00%

Income Taxes - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended			9 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017
Operating Loss Carryforwards [Line Items]
Income tax expense		$ 830	$ 523		$ 32	$ 2,845
Discrete income tax expense (benefit)		$ 200
Discrete tax benefit related to prior year tax reserve releases			$ 600		$ 200	$ 600
Estimated effective income tax rate excluding discrete income tax expense		291.80%	38.80%		35.50%	36.60%
Discrete tax benefit related to Tax Cuts And Jobs Act Of 2017					$ 2,700
Decrease in deferred tax assets				$ 6,600
Increase (decrease) in prepaid taxes				$ 6,600
Prepaid tax asset							$ 5,500
Unrecognized tax benefits		$ 6,700			6,700
Unrecognized tax benefit that would impact effective tax rate		$ 4,000			$ 4,000
Prepaid Expenses and Other Current Assets
Operating Loss Carryforwards [Line Items]
Prepaid tax asset							1,100
Other Long-term Assets
Operating Loss Carryforwards [Line Items]
Prepaid tax asset							$ 4,400
Accounting Standards Update 2016-16
Operating Loss Carryforwards [Line Items]
Increase (decrease) in prepaid taxes	$ (5,500)

Segment and Geographic Information - Revenue by Location and Product Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 102,902	$ 93,281	$ 311,656	$ 285,330
Power discrete
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	83,982	70,794	252,754	212,044
Power IC
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	15,685	19,309	49,540	64,166
Packaging and testing services
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	3,235	3,178	9,362	9,120
Hong Kong
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	84,632	75,785	252,302	236,873
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	15,849	15,334	52,122	42,159
South Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	243	294	831	1,053
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,358	1,075	4,050	2,767
Other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 820	$ 793	$ 2,351	$ 2,478

Segment and Geographic Information - Long-lived Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	$ 258,795	$ 148,191
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	176,433	85,691
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	81,675	61,787
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	$ 687	$ 713

Segment and Geographic Information - Narratives (Details)	9 Months Ended
	Mar. 31, 2018 Segment
Segment Reporting [Abstract]
Number of operating segments	1
Number of reportable segments	1

Commitments and Contingencies - Purchase Commitments (Details) - USD ($)		9 Months Ended
	Sep. 05, 2017	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017
Purchase Commitment, Excluding Long-term Committment [Line Items]
Payments to Acquire Intangible Assets		$ 14,034,000	$ 0
Raw materials, wafers, and packaging and testing services puchase commitments
Purchase Commitment, Excluding Long-term Committment [Line Items]
Purchase commitment, amount		38,400,000		$ 25,700,000
Property and equipment purchase commitments
Purchase Commitment, Excluding Long-term Committment [Line Items]
Purchase commitment, amount		89,600,000		69,200,000
License fees \| STMicro
Purchase Commitment, Excluding Long-term Committment [Line Items]
Payments to Acquire Intangible Assets	$ 17,000,000	13,500,000
Intangible assets		16,400,000
Indemnification Agreement
Purchase Commitment, Excluding Long-term Committment [Line Items]
Indemnifications accrual		$ 0		$ 0

Commitments and Contingencies - Guarantees (Details) - USD ($)	Mar. 31, 2018	Jun. 30, 2017
Indemnification Agreement
Loss Contingencies [Line Items]
Indemnifications accrual	$ 0	$ 0

Commitments and Contingencies - Operating Lease Obligations (Details) $ in Thousands	1 Months Ended
	Apr. 30, 2018 ft²	Mar. 31, 2018 USD ($)
Subsequent Event [Line Items]
2019		$ 96
2020		127
2021		131
2022		135
2023		139
Thereafter		192
Total		$ 820
Subsequent Event
Subsequent Event [Line Items]
Area of leased property \| ft²	5,000
Lease term, in months	76 months

Commitments and Contingencies - Other Investments (Details)	1 Months Ended	15 Months Ended
	Mar. 31, 2016	Mar. 31, 2018 CNY (¥)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jan. 10, 2017 CNY (¥)	Jan. 10, 2017 USD ($)	Mar. 29, 2016 USD ($)
Parent Company \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	51.00%
Chongqing Funds \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions	49.00%
Corporate Joint Venture
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Contractual Obligation, Payment		¥ 358,900,000	$ 57,000,000
Total price payable under EPC Contract						¥ 540,000,000	$ 78,000,000
Contractual Obligation, Due in Second Calendar Year		¥ 181,100,000		$ 28,800,000
Corporate Joint Venture \| Facility in Liangjiang New Area of Chongqing (the 'Joint Venture')
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial capitalization of joint venture								$ 330,000,000
Corporate Joint Venture \| Design Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total price payable under EPC Contract						19,500,000	2,800,000
Corporate Joint Venture \| Construction and Procurement Fees
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total price payable under EPC Contract						¥ 520,500,000	$ 75,200,000
Indemnification Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Indemnifications accrual				$ 0	$ 0

Subsequent Events (Details) - Secured Debt - Subsequent Event $ in Millions	May 01, 2018 USD ($)
Subsequent Event [Line Items]
Line of credit facility, maximum borrowing capacity	$ 17.8
Fixed interest rate	5.04%