Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Dec. 31, 2017	Jan. 31, 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	Dec. 31, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		23,948,076

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Current assets:
Cash and cash equivalents	$ 146,209	$ 115,708
Restricted cash	192	221
Accounts receivable, net	24,283	28,410
Inventories	85,672	76,254
Other current assets	8,942	4,883
Total current assets	265,298	225,476
Property, plant and equipment, net	193,253	148,191
Intangible assets, net	14,599	282
Deferred income tax assets - long-term	4,600	4,594
Other long-term assets	42,801	19,865
Total assets	520,551	398,408
Current liabilities:
Accounts payable	70,521	63,134
Accrued liabilities	51,238	28,386
Income taxes payable	1,280	1,748
Deferred margin	1,386	814
Capital leases	846	828
Total current liabilities	125,271	94,910
Income taxes payable - long-term	941	922
Deferred income tax liabilities	442	2,659
Capital leases - long-term	449	866
Other long-term liabilities	396	502
Total liabilities	127,499	99,859
Commitments and contingencies (Note 10)
Preferred shares, par value $0.002 per share:
Authorized: 10,000 shares, issued and outstanding: none at December 31, 2017 and June 30, 2017	0	0
Common shares, par value $0.002 per share:
Authorized: 50,000 shares, issued and outstanding: 29,856 shares and 23,908 shares, respectively at December 31, 2017 and 29,600 shares and 23,992 shares, respectively at June 30, 2017	60	59
Treasury shares at cost, 5,948 shares at December 31, 2017 and 5,608 shares at June 30, 2017	(55,799)	(49,836)
Additional paid-in capital	212,771	206,332
Accumulated other comprehensive income	2,455	306
Retained earnings	120,023	113,909
Total Alpha and Omega Semiconductor Limited shareholder's equity	279,510	270,770
Noncontrolling interest	113,542	27,779
Total equity	393,052	298,549
Total liabilities and equity	$ 520,551	$ 398,408

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	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)	29,856,000	29,600,000
Common stock, shares outstanding (in shares)	23,908,000	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)	5,948,000	5,608,000

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Revenue	$ 103,896	$ 94,687	$ 208,754	$ 192,049
Cost of goods sold	75,814	72,593	153,142	148,011
Gross profit	28,082	22,094	55,612	44,038
Operating expenses
Research and development	9,102	7,284	17,427	14,303
Selling, general and administrative	15,756	11,974	30,371	23,157
Total operating expenses	24,858	19,258	47,798	37,460
Operating income	3,224	2,836	7,814	6,578
Interest income and other loss, net	(160)	(70)	(120)	(119)
Interest expense	(14)	(24)	(31)	(50)
Net income before income taxes	3,050	2,742	7,663	6,409
Income tax expense (benefit)	(2,072)	1,085	(798)	2,322
Net income including noncontrolling interest	5,122	1,657	8,461	4,087
Net loss attributable to noncontrolling interest	(1,669)	(1,190)	(3,130)	(2,067)
Net income attributable to Alpha and Omega Semiconductor Limited	$ 6,791	$ 2,847	$ 11,591	$ 6,154
Net income per common share attributable to Alpha and Omega Semiconductor Limited
Basic (in dollars per share)	$ 0.28	$ 0.12	$ 0.48	$ 0.26
Diluted (in dollars per share)	$ 0.27	$ 0.11	$ 0.46	$ 0.25
Weighted average number of common shares attributable to Alpha and Omega Semiconductor Limited used to compute net income per share
Basic (in shares)	23,925	23,481	23,973	23,256
Diluted (in shares)	25,033	24,977	24,997	24,695

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Net income including noncontrolling interest	$ 5,122	$ 1,657	$ 8,461	$ 4,087
Net income attributable to Alpha and Omega Semiconductor Limited	6,791	2,847	11,591	6,154
Foreign currency translation adjustment	3,347	(2,326)	4,048	(2,256)
Comprehensive income (loss)	8,469	(669)	12,509	1,831
Noncontrolling interest	(104)	(2,234)	(1,231)	(3,132)
Comprehensive income attributable to Alpha and Omega Semiconductor Limited	$ 8,573	$ 1,565	$ 13,740	$ 4,963

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income including noncontrolling interest	$ 8,461	$ 4,087
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	14,386	13,263
Share-based compensation expense	6,017	2,870
Deferred income taxes, net	(2,224)	6,581
Loss (Gain) on disposal of property and equipment	55	(370)
Changes in assets and liabilities:
Accounts receivable, net	4,127	2,112
Inventories	(9,418)	(1,391)
Other current and long-term assets	(9,081)	(7,032)
Accounts payable	1,877	(4,605)
Income taxes payable	(448)	257
Accrued and other liabilities	8,102	2,297
Net cash provided by operating activities	21,854	18,069
Cash flows from investing activities
Purchases of property and equipment excluding JV Company	(23,192)	(11,371)
Purchases of property and equipment in JV Company	(41,576)	(3,632)
Purchases of land use rights in JV Company	0	(8,737)
Purchase of intangible assets	(10,384)	0
Proceeds from sale of property and equipment	0	411
(Increase) decrease in restricted cash	29	(135)
Net cash used in investing activities	(75,123)	(23,464)
Cash flows from financing activities
Proceeds from investment by noncontrolling interest	86,994	33,000
Withholding tax on restricted stock units	(249)	(348)
Proceeds from exercise of stock options and ESPP	2,205	8,729
Payments for Repurchase of Common Stock	6,022	0
Principal payments on capital leases	(399)	(408)
Net cash provided by financing activities	82,529	40,973
Effect of exchange rate changes on cash and cash equivalents	1,241	(559)
Net increase in cash and cash equivalents	30,501	35,019
Cash and cash equivalents at beginning of period	115,708	87,774
Cash and cash equivalents at end of period	146,209	122,793
Supplemental disclosures of non-cash investing and financing information:
Property and equipment purchased but not yet paid	43,235	5,153
Re-issuance of treasury stock	$ 3	$ 59

Intangible assets, net (Parentheticals) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 17,002	$ 2,666
Less: accumulated amortization	(2,672)	(2,653)
License fees
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	15,584	1,248
Intangible assets, net	13,800
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	6 Months Ended
The Company and Significant Accounting Policies	Dec. 31, 2017
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 six months ended December 31, 2017 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 Accounting Standard Updates ("ASU") 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, the vesting conditions, 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. 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 standards in its first quarter of fiscal year 2019 utilizing the modified retrospective method. The Company is still in the process of completing its analysis on the transition of all revenue from distributors from sell-through to the sell-in basis of accounting, as well as impact of related disclosures and its internal controls over financial reporting.

Net Income (Loss) Per Share

6 Months Ended

Dec. 31, 2017

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 December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands, except per share data)
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$	6,791	$	2,847	$	11,591	$	6,154

Denominator:
Basic:
Weighted average number of common shares used to compute basic net income per share	23,925		23,481		23,973		23,256
Diluted:
Weighted average number of common shares used to compute basic net income per share	23,925		23,481		23,973		23,256
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	1,108		1,496		1,024		1,439
Weighted average number of common shares used to compute diluted net income per share	25,033		24,977		24,997		24,695
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic	$	0.28	$	0.12	$	0.48	$	0.26
Diluted	$	0.27	$	0.11	$	0.46	$	0.25

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 December 31,		Six Months Ended December 31,
	2017	2016	2017	2016
	(in thousands)		(in thousands)
Employee stock options and RSUs	165	—	169	123
ESPP	—	16	45	8
Total potential dilutive securities	165	16	214	131

Concentration of Credit Risk and Significant Customers

6 Months Ended

Dec. 31, 2017

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 December 31,				Six Months Ended December 31,
Percentage of revenue	2017		2016		2017		2016
Customer A	30.8	%	27.0	%	29.2	%	25.6	%
Customer B	33.7	%	35.8	%	33.8	%	36.2	%
Customer C	*		10.7	%	*		12.3	%

* Less than 10%



	December 31, 2017		June 30, 2017
Percentage of accounts receivable	December 31, 2017		June 30, 2017
Customer A	35.7	%	33.2	%
Customer B	19.1	%	13.2	%
Customer C	12.6	%	16.4	%

Balance Sheet Components

6 Months Ended

Dec. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Components

Accounts receivable, net:



	December 31, 2017			June 30, 2017
	(in thousands)
Accounts receivable	$	45,438		$	48,039
Less: Allowance for price adjustments	(21,125		)	(19,599		)
Less: Allowance for doubtful accounts	(30		)	(30		)
Accounts receivable, net	$	24,283		$	28,410

Inventories:



	December 31, 2017		June 30, 2017
	(in thousands)
Raw materials	$	39,198	$	32,118
Work in-process	34,994		36,081
Finished goods	11,480		8,055
	$	85,672	$	76,254

Property, plant and equipment, net:



	December 31, 2017			June 30, 2017
	(in thousands)
Land	$	4,877		$	4,877
Building	4,325			4,325
Manufacturing machinery and equipment	241,206			215,275
Equipment and tooling	14,641			13,549
Computer equipment and software	25,066			24,346
Office furniture and equipment	2,055			1,935
Leasehold improvements	29,507			29,136
Land use rights	9,242			8,849
	330,919			302,292
Less: accumulated depreciation	(212,058		)	(194,882		)
	118,861			107,410
Equipment and construction in progress	74,392			40,781
Property, plant and equipment, net	$	193,253		$	148,191

Intangible assets, net:



	December 31, 2017			June 30, 2017
	(in thousands)
License fees	$	15,584		$	1,248
Trade name	268			268
Customer relationships	1,150			1,150
	17,002			2,666
Less: accumulated amortization	(2,672		)	(2,653		)
	14,330			13
Goodwill	269			269
Intangible assets, net	$	14,599		$	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 December 31, 2017, the Company recorded $13.8 million in intangible assets, of which $9.8 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:



	December 31, 2017		June 30, 2017
	(in thousands)
Prepayments for property and equipment	$	36,359	$	12,964
Investment in a privately held company	700		700
Prepaid income tax	—		4,377
Long-term deposits	5,386		1,608
Other	356		216
	$	42,801	$	19,865

Accrued liabilities:



	December 31, 2017		June 30, 2017
	(in thousands)
Accrued compensation and benefits	$	21,963	$	13,727
Warranty accrual	767		1,866
Stock rotation accrual	1,611		1,871
Accrued professional fees	1,856		2,500
Accrued inventory	1,008		410
Accrued facilities related expenses	1,820		1,501
Accrued property, plant and equipment	16,321		2,241
Other accrued expenses	5,892		4,270
	$	51,238	$	28,386

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



	Six Months Ended December 31,
	2017				2016
	(in thousands)
Beginning balance	$	1,866			$	1,495
Additions (Reductions)	(1,063		)	*	1,040
Utilization	(36		)		(153		)
Ending balance	$	767			$	2,382

* Released a specific warranty reserve of approximately $1.0 million due to expired warranty period.

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



	Six Months Ended December 31,
	2017			2016
	(in thousands)
Beginning balance	$	1,871		$	1,988
Additions	992			3,008
Utilization	(1,252		)	(3,289		)
Ending balance	$	1,611		$	1,707

Debt Debt	6 Months Ended
Debt Debt	Dec. 31, 2017
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 provides 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 of 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. As of December 31, 2017, the Company recorded approximately $0.1 million of transaction costs.

Joint Venture

6 Months Ended

Dec. 31, 2017

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. 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 Company expects the JV Company to commence initial production in mid-calendar year 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 December 31, 2017, the JV Company paid approximately $37.0 million (RMB 243.8 million), and expects to pay the remaining of $44.9 million (RMB 296.2 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	827			—			827
Reissuance of treasury stock upon exercise of common stock options and release of RSUs	(61		)	—			(61		)
Withholding tax on restricted stock units	(249		)	—			(249		)
Issuance of shares under ESPP	1,439			—			1,439
Repurchase of common shares under shares repurchase program	(6,022		)	—			(6,022		)
Stock-based compensation expense	4,546			—			4,546
Net income (loss)	11,591			(3,130		)	8,461
Deferred tax asset related to ASU 2016-16 adoption	(5,480		)	—			(5,480		)
Cumulative translation adjustment	2,149			1,899			4,048
Contributions from noncontrolling interest	—			86,994			86,994
Balance, December 31, 2017	$	279,510		$	113,542		$	393,052

Shareholders' Equity and Share-based Compensation

6 Months Ended

Dec. 31, 2017

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 six months ended December 31, 2017, the Company repurchased an aggregate of 346,621 shares from the open market, for a total cost of $6.0 million, at an average price of $17.34 per share. Since the inception of the prior repurchase program in 2010, the Company repurchased an aggregate of 6,069,714 shares from the open market including shares purchased in a dutch tender offer for a total cost of $56.8 million, at an average price of $9.35 per share, excluding fees and related expenses. No repurchased shares have been retired. Of the 6,069,714 repurchased shares, 122,154 shares with a weighted average repurchase price of $10.70 per share, were reissued at an average price of $6.06 per share pursuant to option exercises and vested restricted share units. As of December 31, 2017, approximately $24.0 million remained available under the Repurchase Program.

Stock Options

The Company did not grant any stock options during the six months ended December 31, 2017. 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 six months ended December 31, 2017:



					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
Granted	—		$	—
Exercised	(64,521	)	$	11.85		$	344,085
Canceled or forfeited	—		$	—
Outstanding at December 31, 2017	988,846		$	10.92	4.17	$	5,646,519
Options vested and expected to vest	988,473		$	10.92	4.16	$	5,643,340
Exercisable at December 31, 2017	953,428		$	11.04	4.09	$	5,337,845

Restricted Stock Units ("RSU")

The following table summarizes the Company's RSU activities for the six months ended December 31, 2017:



	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	93,907		$	17.25
Vested	(64,312	)	$	14.20
Forfeited	(17,900	)	$	14.03
Nonvested at December 31, 2017	1,156,560		$	14.36	1.36	$	18,921,322
RSUs vested and expected to vest	1,050,575				1.28	$	17,187,413

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

In March 2017, the Company granted 170,000 performance-based RSUs (“PRSUs”) to its key personnel. The number shares to be issued under the PRSU will be determined based on the level of attainment of predetermined financial goals. The PRSU will vest in four equal annual installments from March 15, 2018 if certain predetermined financial goals were met. The Company recorded approximately $0.5 million and $0.7 million of expenses for these PRSUs during the three and six months ended December 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 will 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 $1.5 million of such RSUs expenses in the three months ended December 31, 2017. The expenses are reported in the accrued liabilities line in the condensed consolidated balance sheet as the total amount of bonus is to be settled in variable number of shares. Such non-cash compensation expenses are recorded as part of stock-based compensation expense in the condensed consolidated statements of operations.

Employee Share Purchase Plan ("ESPP")

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




	Six Months Ended December 31,
	2017
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 December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Cost of goods sold	$	415	$	205	$	731	$	400
Research and development	617		383		979		743
Selling, general and administrative	2,977		966		4,307		1,727
	$	4,009	$	1,554	$	6,017	$	2,870

As of December 31, 2017, total unrecognized compensation cost under the Company's equity plans was $9.7 million, which is expected to be recognized over a weighted-average period of 1.2 years.

Income Taxes	6 Months Ended
Income Taxes	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes For the three months ended December 31, 2017, the Company recognized income tax benefit of approximately $2.1 million, which included a discrete tax benefit of $2.7 million related to re-measuring 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. For the three months ended December 31, 2016, the Company recognized income tax expense of approximately $1.1 million. Excluding the discrete income tax items, the estimated effective tax rate for the three months ended December 31, 2017 was 31.4% compared to 39.1% for the three months ended December 31, 2016. 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 six months ended December 31, 2017, the Company recognized an income tax benefit of approximately $0.8 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. For the six months ended December 31, 2016, the Company recognized income tax expense of approximately $2.3 million. Excluding the discrete income tax items, the estimated effective tax rate for the six months ended December 31, 2017 was 24.0% compared to 35.6% for the six months ended December 31, 2016. 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 December 31, 2017, the gross amount of unrecognized tax benefits was approximately $6.8 million, of which $4.1 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 December 31, 2017. The Company will continue to monitor ongoing developments and potential impacts to its financial statements.

Segment and Geographic Information

6 Months Ended

Dec. 31, 2017

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 to:



	Three Months Ended December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Hong Kong	$	82,440	$	78,253	$	167,670	$	161,088
China	19,153		14,383		36,273		26,825
South Korea	301		393		588		759
United States	1,314		798		2,692		1,692
Other Countries	688		860		1,531		1,685
	$	103,896	$	94,687	$	208,754	$	192,049

The following is a summary of revenue by product type:



	Three Months Ended December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Power discrete	$	85,094	$	69,822	$	168,772	$	141,250
Power IC	15,758		21,859		33,855		44,857
Packaging and testing services	3,044		3,006		6,127		5,942
	$	103,896	$	94,687	$	208,754	$	192,049

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



	December 31, 2017		June 30, 2017
	(in thousands)
China	$	123,885	$	85,691
United States	68,701		61,787
Other Countries	667		713
	$	193,253	$	148,191

Commitments and Contingencies	6 Months Ended
Commitments and Contingencies	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Purchase Commitments As of December 31, 2017 and June 30, 2017, the Company had approximately $34.7 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 $128.7 million and $69.2 million, respectively, of capital commitments for the purchase of property and equipment and EPC construction. 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 December 31, 2017 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.

The Company and Significant Accounting Policies (Policies)	6 Months Ended
	Dec. 31, 2017
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 six months ended December 31, 2017 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 Accounting Standard Updates ("ASU") 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, the vesting conditions, 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. 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 standards in its first quarter of fiscal year 2019 utilizing the modified retrospective method. The Company is still in the process of completing its analysis on the transition of all revenue from distributors from sell-through to the sell-in basis of accounting, as well as impact of related disclosures and its internal controls over financial reporting.
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)

6 Months Ended

Dec. 31, 2017

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 December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands, except per share data)
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$	6,791	$	2,847	$	11,591	$	6,154

Denominator:
Basic:
Weighted average number of common shares used to compute basic net income per share	23,925		23,481		23,973		23,256
Diluted:
Weighted average number of common shares used to compute basic net income per share	23,925		23,481		23,973		23,256
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	1,108		1,496		1,024		1,439
Weighted average number of common shares used to compute diluted net income per share	25,033		24,977		24,997		24,695
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic	$	0.28	$	0.12	$	0.48	$	0.26
Diluted	$	0.27	$	0.11	$	0.46	$	0.25

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 December 31,		Six Months Ended December 31,
	2017	2016	2017	2016
	(in thousands)		(in thousands)
Employee stock options and RSUs	165	—	169	123
ESPP	—	16	45	8
Total potential dilutive securities	165	16	214	131

Concentration of Credit Risk and Significant Customers (Tables)

6 Months Ended

Dec. 31, 2017

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 December 31,				Six Months Ended December 31,
Percentage of revenue	2017		2016		2017		2016
Customer A	30.8	%	27.0	%	29.2	%	25.6	%
Customer B	33.7	%	35.8	%	33.8	%	36.2	%
Customer C	*		10.7	%	*		12.3	%

* Less than 10%



	December 31, 2017		June 30, 2017
Percentage of accounts receivable	December 31, 2017		June 30, 2017
Customer A	35.7	%	33.2	%
Customer B	19.1	%	13.2	%
Customer C	12.6	%	16.4	%

Balance Sheet Components (Tables)

6 Months Ended

Dec. 31, 2017

Balance Sheet Related Disclosures [Abstract]

Schedule of Accounts, Notes, Loans and Financing Receivable

Accounts receivable, net:



	December 31, 2017			June 30, 2017
	(in thousands)
Accounts receivable	$	45,438		$	48,039
Less: Allowance for price adjustments	(21,125		)	(19,599		)
Less: Allowance for doubtful accounts	(30		)	(30		)
Accounts receivable, net	$	24,283		$	28,410

Schedule of Inventory, Current

Inventories:



	December 31, 2017		June 30, 2017
	(in thousands)
Raw materials	$	39,198	$	32,118
Work in-process	34,994		36,081
Finished goods	11,480		8,055
	$	85,672	$	76,254

Property, Plant and Equipment

Property, plant and equipment, net:



	December 31, 2017			June 30, 2017
	(in thousands)
Land	$	4,877		$	4,877
Building	4,325			4,325
Manufacturing machinery and equipment	241,206			215,275
Equipment and tooling	14,641			13,549
Computer equipment and software	25,066			24,346
Office furniture and equipment	2,055			1,935
Leasehold improvements	29,507			29,136
Land use rights	9,242			8,849
	330,919			302,292
Less: accumulated depreciation	(212,058		)	(194,882		)
	118,861			107,410
Equipment and construction in progress	74,392			40,781
Property, plant and equipment, net	$	193,253		$	148,191

Intangible Assets Disclosure

Intangible assets, net:



	December 31, 2017			June 30, 2017
	(in thousands)
License fees	$	15,584		$	1,248
Trade name	268			268
Customer relationships	1,150			1,150
	17,002			2,666
Less: accumulated amortization	(2,672		)	(2,653		)
	14,330			13
Goodwill	269			269
Intangible assets, net	$	14,599		$	282

Schedule of Other Assets, Noncurrent

Other long-term assets:



	December 31, 2017		June 30, 2017
	(in thousands)
Prepayments for property and equipment	$	36,359	$	12,964
Investment in a privately held company	700		700
Prepaid income tax	—		4,377
Long-term deposits	5,386		1,608
Other	356		216
	$	42,801	$	19,865

Schedule of Accrued Liabilities

Accrued liabilities:



	December 31, 2017		June 30, 2017
	(in thousands)
Accrued compensation and benefits	$	21,963	$	13,727
Warranty accrual	767		1,866
Stock rotation accrual	1,611		1,871
Accrued professional fees	1,856		2,500
Accrued inventory	1,008		410
Accrued facilities related expenses	1,820		1,501
Accrued property, plant and equipment	16,321		2,241
Other accrued expenses	5,892		4,270
	$	51,238	$	28,386

Schedule of Product Warranty Liability

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



	Six Months Ended December 31,
	2017				2016
	(in thousands)
Beginning balance	$	1,866			$	1,495
Additions (Reductions)	(1,063		)	*	1,040
Utilization	(36		)		(153		)
Ending balance	$	767			$	2,382

Stock Rotation Accrual

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



	Six Months Ended December 31,
	2017			2016
	(in thousands)
Beginning balance	$	1,871		$	1,988
Additions	992			3,008
Utilization	(1,252		)	(3,289		)
Ending balance	$	1,611		$	1,707

Joint Venture (Tables)

6 Months Ended

Dec. 31, 2017

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	827			—			827
Reissuance of treasury stock upon exercise of common stock options and release of RSUs	(61		)	—			(61		)
Withholding tax on restricted stock units	(249		)	—			(249		)
Issuance of shares under ESPP	1,439			—			1,439
Repurchase of common shares under shares repurchase program	(6,022		)	—			(6,022		)
Stock-based compensation expense	4,546			—			4,546
Net income (loss)	11,591			(3,130		)	8,461
Deferred tax asset related to ASU 2016-16 adoption	(5,480		)	—			(5,480		)
Cumulative translation adjustment	2,149			1,899			4,048
Contributions from noncontrolling interest	—			86,994			86,994
Balance, December 31, 2017	$	279,510		$	113,542		$	393,052

Shareholders' Equity and Share-based Compensation (Tables)

6 Months Ended

Dec. 31, 2017

Share-based Compensation [Abstract]

Summary of Stock Option Activities

Stock Options

The Company did not grant any stock options during the six months ended December 31, 2017. 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 six months ended December 31, 2017:



					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
Granted	—		$	—
Exercised	(64,521	)	$	11.85		$	344,085
Canceled or forfeited	—		$	—
Outstanding at December 31, 2017	988,846		$	10.92	4.17	$	5,646,519
Options vested and expected to vest	988,473		$	10.92	4.16	$	5,643,340
Exercisable at December 31, 2017	953,428		$	11.04	4.09	$	5,337,845

Restricted Stock Units Activity

Restricted Stock Units ("RSU")

The following table summarizes the Company's RSU activities for the six months ended December 31, 2017:



	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	93,907		$	17.25
Vested	(64,312	)	$	14.20
Forfeited	(17,900	)	$	14.03
Nonvested at December 31, 2017	1,156,560		$	14.36	1.36	$	18,921,322
RSUs vested and expected to vest	1,050,575				1.28	$	17,187,413

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:




	Six Months Ended December 31,
	2017
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 December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Cost of goods sold	$	415	$	205	$	731	$	400
Research and development	617		383		979		743
Selling, general and administrative	2,977		966		4,307		1,727
	$	4,009	$	1,554	$	6,017	$	2,870

Segment and Geographic Information (Tables)

6 Months Ended

Dec. 31, 2017

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:



	December 31, 2017		June 30, 2017
	(in thousands)
China	$	123,885	$	85,691
United States	68,701		61,787
Other Countries	667		713
	$	193,253	$	148,191

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



	Three Months Ended December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Hong Kong	$	82,440	$	78,253	$	167,670	$	161,088
China	19,153		14,383		36,273		26,825
South Korea	301		393		588		759
United States	1,314		798		2,692		1,692
Other Countries	688		860		1,531		1,685
	$	103,896	$	94,687	$	208,754	$	192,049

Revenue from External Customers by Products and Services

The following is a summary of revenue by product type:



	Three Months Ended December 31,				Six Months Ended December 31,
	2017		2016		2017		2016
	(in thousands)				(in thousands)
Power discrete	$	85,094	$	69,822	$	168,772	$	141,250
Power IC	15,758		21,859		33,855		44,857
Packaging and testing services	3,044		3,006		6,127		5,942
	$	103,896	$	94,687	$	208,754	$	192,049

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		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Numerator:
Net income attributable to Alpha and Omega Semiconductor Limited	$ 6,791	$ 2,847	$ 11,591	$ 6,154
Basic:
Weighted average number of common shares used to compute basic net income per share	23,925	23,481	23,973	23,256
Effect of potentially dilutive securities:
Stock options, RSUs and ESPP shares	1,108	1,496	1,024	1,439
Weighted average number of common shares used to compute diluted net income per share	25,033	24,977	24,997	24,695
Net income per share attributable to Alpha and Omega Semiconductor Limited:
Basic (in dollars per share)	$ 0.28	$ 0.12	$ 0.48	$ 0.26
Diluted (in dollars per share)	$ 0.27	$ 0.11	$ 0.46	$ 0.25

Net Income (Loss) Per Share - Potential Dilutive Shares (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	165	16	214	131
Employee stock options and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	165	0	169	123
ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential dilutive securities (in shares)	0	16	45	8

Concentration of Credit Risk and Significant Customers - (Details)

3 Months Ended

6 Months Ended

Dec. 31, 2017

Jun. 30, 2017

Dec. 31, 2016

Dec. 31, 2017

Dec. 31, 2016

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

30.80%

27.00%

29.20%

25.60%

Customer A | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

35.70%

33.20%

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

Concentration Risk

Customers greater than 10% of total

33.70%

35.80%

33.80%

36.20%

Customer B | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

19.10%

13.20%

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

Concentration Risk

Customers greater than 10% of total

10.70%

^[1]

12.30%

Customer C | Accounts Receivable | Customer Concentration Risk

Concentration Risk

Customers greater than 10% of total

12.60%

16.40%

[1]	* Less than 10%

Balance Sheet Components - Accounts receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Accounts receivable	$ 45,438	$ 48,039
Less: Allowance for price adjustments	(21,125)	(19,599)
Less: Allowance for doubtful accounts	(30)	(30)
Accounts receivable, net	$ 24,283	$ 28,410

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Raw materials	$ 39,198	$ 32,118
Work in-process	34,994	36,081
Finished goods	11,480	8,055
Inventory, net	$ 85,672	$ 76,254

Balance Sheet Components - Property, plant, and equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	$ 330,919	$ 302,292
Land Use Rights, Gross	9,242	8,849
Less: accumulated depreciation	(212,058)	(194,882)
Property, plant and equipment excluding equipment and construction in progress, net	118,861	107,410
Equipment and construction in progress	74,392	40,781
Property, plant and equipment, net	193,253	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	241,206	215,275
Equipment and tooling
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	14,641	13,549
Computer equipment and software
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	25,066	24,346
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	2,055	1,935
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant, and equipment excluding equipment and construction In progress, gross	$ 29,507	$ 29,136

Balance Sheet Components - Intangible assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	$ 17,002	$ 2,666
Less: accumulated amortization	(2,672)	(2,653)
Intangible Assets, Net (Excluding Goodwill)	14,330	13
Goodwill	269	269
Intangible assets, net	14,599	282
License fees
Schedule of Finite-lived Intangible Assets and Goodwill [Line Items]
Finite-Lived Intangible Assets, Gross	15,584	1,248
Finite-Lived Intangible Assets, Net	13,800
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	$ 9,800

Balance Sheet Components - Intangible Assets, Additional Information (Details) - USD ($) $ in Thousands		6 Months Ended
	Sep. 05, 2017	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Intangible Assets		$ 10,384	$ 0
License fees
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Net		13,800
STMicro \| License fees
Finite-Lived Intangible Assets [Line Items]
Payments to Acquire Intangible Assets	$ 17,000
Payments to Acquire Intangible Assets, Remainder of Calendar Year	10,100
Payments to Acquire Intangible Assets, Calendar Year Two	6,700
Payments to Acquire Intangible Assets, Calendar Year Three	$ 200
Finite-Lived Intangible Assets, Net		$ 9,800

Balance Sheet Components - Other long term assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Prepayments for property and equipment	$ 36,359	$ 12,964
Investment in a privately held company	700	700
Prepaid income tax	0	4,377
Long-term deposits	5,386	1,608
Other	356	216
Other long-term assets	$ 42,801	$ 19,865

Balance Sheet Components - Accrued liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Balance Sheet Related Disclosures [Abstract]
Accrued compensation and benefits	$ 21,963	$ 13,727
Warranty accrual	767	1,866	$ 2,382	$ 1,495
Stock rotation accrual	1,611	1,871	$ 1,707	$ 1,988
Accrued professional fees	1,856	2,500
Accrued inventory	1,008	410
Accrued facilities related expenses	1,820	1,501
Accrued property, plant and equipment	16,321	2,241
Other accrued expenses	5,892	4,270
Accrued liabilities	$ 51,238	$ 28,386

Balance Sheet Components - Product Warranty Accrual (Details) - USD ($) $ in Thousands	6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Beginning balance	$ 1,866	$ 1,495
Additions (Reductions)	(1,063)	1,040
Utilization	(36)	(153)
Ending balance	767	$ 2,382
Release of specific warranty reserve	$ 1,000

Balance Sheet Components - Stock Rotation Accrual (Details) - USD ($) $ in Thousands	6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Stock Rotation Accrual Increae (Decrease) [Roll Forward]
Beginning balance	$ 1,871	$ 1,988
Additions	992	3,008
Utilization	(1,252)	(3,289)
Ending balance	$ 1,611	$ 1,707

Debt (Details) - Term Loan - Secured Debt - Variable Interest Rate Term Loan Maturing August 2022 - USD ($) $ in Millions	Aug. 15, 2017	Jan. 12, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 30.0
Debt instrument, term	5 years
Transaction costs			$ 0.1
Subsequent Event
Debt Instrument [Line Items]
Amount outstanding		$ 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		6 Months Ended		12 Months Ended
Joint Venture - Narrative (Details) $ in Thousands	Sep. 30, 2016 USD ($)	Mar. 31, 2016	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2017 CNY (¥)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Jan. 10, 2017 CNY (¥)	Jan. 10, 2017 USD ($)	Mar. 29, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
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					¥ 243,800,000	$ 37,000
Contract amount payable in calendar year 2018					¥ 296,200,000		$ 44,900
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

Joint Venture - Changes in Total Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		86 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Balance, June 30, 2017			$ 298,549
Exercise of common stock options and release of RSUs			827
Reissuance of treasury stock upon exercise of common stock options and release of RSUs			(61)
Withholding tax on restricted stock units			(249)
Issuance of shares under ESPP			1,439
Repurchase of common shares under shares repurchase program			(6,022)		$ (56,800)
Stock-based compensation expense			4,546
Net income (loss)	$ 5,122	$ 1,657	8,461	$ 4,087
Net loss attributable to noncontrolling interest	(1,669)	$ (1,190)	(3,130)	(2,067)
Cumulative translation adjustment			4,048
Contributions from noncontrolling interest			86,994	$ 33,000
Balance, December 31, 2017	393,052		393,052		393,052
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			827
Reissuance of treasury stock upon exercise of common stock options and release of RSUs			(61)
Withholding tax on restricted stock units			(249)
Issuance of shares under ESPP			1,439
Repurchase of common shares under shares repurchase program			(6,022)
Stock-based compensation expense			4,546
Net income (loss)			11,591
Cumulative translation adjustment			2,149
Contributions from noncontrolling interest			0
Balance, December 31, 2017	279,510		279,510		279,510
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			(3,130)
Cumulative translation adjustment			1,899
Contributions from noncontrolling interest			86,994
Balance, December 31, 2017	$ 113,542		113,542		$ 113,542
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) $ / shares in Units, $ in Thousands	6 Months Ended	86 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Class of Stock [Line Items]
Share repurchase program, authorized amount (USD in Millions) \| $	$ 30,000	$ 30,000
Shares Repurchase Program Remaining Balance \| $	$ 24,000	$ 24,000
Repurchase of common shares under shares repurchase program	346,621	6,069,714
Repurchase of common shares under shares repurchase program \| $	$ (6,022)	$ (56,800)
Treasury stock acquired, average price per share (in dollars per share) \| $ / shares	$ 17.34	$ 9.35
Treasury Stock, Shares, Retired	0
Treasury Stock Reissued, Average Price Per Share \| $ / shares		6.06
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Treasury Stock Reissued
Class of Stock [Line Items]
Treasury stock acquired, average price per share (in dollars per share) \| $ / shares		$ 10.70
Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures (in shares)		122,154

Shareholders' Equity and Share-based Compensation - Share-based Compensation (Details) - USD ($)	3 Months Ended		6 Months Ended	86 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common shares under shares repurchase program			346,621	6,069,714
Options, Weighted-Average Remaining Contractual Life (in years)		4 years 5 months 5 days	4 years 2 months 1 day
Options vested and expected to vest, Number Outstanding (in shares)	988,473		988,473	988,473
Options vested and expected to vest, Weighted Average Exercise Price (in dollars per share)	$ 10.92		$ 10.92	$ 10.92
Options vested and expected to vest, Weighted Average Remaining Contractual Life (in years)			4 years 1 month 28 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding, Aggregate Intrinsic Value	$ 5,643,340		$ 5,643,340	$ 5,643,340
Options, Number Exercisable (in shares)	953,428		953,428	953,428
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price	$ 11.04		$ 11.04	$ 11.04
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	4 years 1 month 2 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 5,337,845		$ 5,337,845	$ 5,337,845
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)			(64,521)
Canceled or forfeited (in shares)			0
Outstanding at December 31, 2017	988,846	1,053,367	988,846	988,846
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
Granted (in dollars per share)			0
Exercised (in dollars per share)			11.85
Canceled or forfeited (in dollars per share)			0
Outstanding at December 31, 2017 (in dollars per share)	$ 10.92	$ 10.98	$ 10.92	$ 10.92
Options Outstanding Aggregate Intrinsic Value	$ 5,646,519	$ 6,212,660	$ 5,646,519	$ 5,646,519
Options Exercised Aggregate Intrinsic Value			$ 344,085
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	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2017
Share-based Compensation [Abstract]
Options, Number Outstanding (in shares)	1,053,367	988,846
Options, Weighted-Average Remaining Contractual Life (in years)	4 years 5 months 5 days	4 years 2 months 1 day
Options, Weighted-Average Exercise Price (in dollars per share)	$ 10.98	$ 10.92
Options, Number Exercisable (in shares)		953,428
Options, Weighted-Average Exercise Price (in dollars per share)		$ 11.04
Options vested and expected to vest, Number Outstanding (in shares)		988,473
Options vested and expected to vest, Weighted Average Remaining Contractual Life (in years)		4 years 1 month 28 days
Options vested and expected to vest, Weighted Average Exercise Price (in dollars per share)		$ 10.92

Shareholders' Equity and Share-based Compensation - Restricted Stock Activity (Details) - USD ($)	3 Months Ended				6 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
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 2 months 12 days
Allocated share-based compensation expense	$ 4,009,000			$ 1,554,000	$ 6,017,000	$ 2,870,000
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					93,907
Vested					(64,312)
Forfeited					(17,900)
Nonvested at December 31, 2017	1,156,560	1,144,865			1,156,560
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					17.25
Vested					14.20
Forfeited					14.03
Nonvested at December 31, 2017	$ 14.36	$ 14.11			$ 14.36
Weighted Average Remaining Recognition Period (Years)	1 year 4 months 10 days	1 year 9 months 4 days
RSUs Nonvested Aggregate Intrinsic Value	$ 18,921,322	$ 19,084,900			$ 18,921,322
RSUs vested and expected to vest, Outstanding (in shares)	1,050,575				1,050,575
RSUs vested and expected to vest, Weighted Average Remaining Recognition Period (in years)	1 year 3 months 11 days
RSUs vested and expected to vest, Aggregate Intrinsic Value	$ 17,187,413				$ 17,187,413
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			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	$ 500,000				$ 700,000

Shareholders' Equity and Share-based Compensation - Share-based Compensation Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Nov. 15, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 4,009	$ 1,554	$ 6,017	$ 2,870
Unrecognized compensation expense	$ 9,700		9,700
Recognition period of share-based compensation expense (in years)	1 year 2 months 12 days
Cost of goods sold
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	$ 415	205	731	400
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	617	383	979	743
Selling, general and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Allocated share-based compensation expense	2,977	$ 966	$ 4,307	$ 1,727
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	$ 1,500
Incentive award payable in shares, percent of total award (up to 50%)					50.00%

Income Taxes - Narrative (Details) - USD ($) $ in Thousands		3 Months Ended			6 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Operating Loss Carryforwards [Line Items]
Income tax expense (benefit)		$ (2,072)	$ 1,085		$ (798)	$ 2,322
Discrete income tax expense (benefit)		$ 2,700			$ 2,700
Estimated effective income tax rate excluding discrete income tax expense		31.40%	39.10%		24.00%	35.60%
Decrease in deferred tax assets				$ 6,600
Prepaid taxes							$ 5,500
Increase (decrease) in prepaid taxes				$ 6,600
Unrecognized tax benefits		$ 6,800			$ 6,800
Unrecognized tax benefit that would impact effective tax rate		$ 4,100			$ 4,100
Prepaid Expenses and Other Current Assets
Operating Loss Carryforwards [Line Items]
Prepaid taxes							1,100
Other Long-term Assets
Operating Loss Carryforwards [Line Items]
Prepaid taxes							$ 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		6 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 103,896	$ 94,687	$ 208,754	$ 192,049
Power discrete
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	85,094	69,822	168,772	141,250
Power IC
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	15,758	21,859	33,855	44,857
Packaging and testing services
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	3,044	3,006	6,127	5,942
Hong Kong
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	82,440	78,253	167,670	161,088
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	19,153	14,383	36,273	26,825
South Korea
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	301	393	588	759
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	1,314	798	2,692	1,692
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 688	$ 860	$ 1,531	$ 1,685

Segment and Geographic Information - Long-lived Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Jun. 30, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	$ 193,253	$ 148,191
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	123,885	85,691
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	68,701	61,787
Other Countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Property, plant and equipment, net and land use rights, net	$ 667	$ 713

Segment and Geographic Information - Narratives (Details)	6 Months Ended
	Dec. 31, 2017 Segment
Segment Reporting [Abstract]
Number of operating segments	1
Number of reportable segments	1

Commitments and Contingencies - Purchase Commitments (Details) - USD ($)		6 Months Ended
	Sep. 05, 2017	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2017
Purchase Commitment, Excluding Long-term Committment [Line Items]
Payments to Acquire Intangible Assets		$ 10,384,000	$ 0
Raw materials, wafers, and packaging and testing services puchase commitments
Purchase Commitment, Excluding Long-term Committment [Line Items]
Purchase commitment, amount		34,700,000		$ 25,700,000
Property and equipment purchase commitments
Purchase Commitment, Excluding Long-term Committment [Line Items]
Purchase commitment, amount		128,700,000		69,200,000
License fees
Purchase Commitment, Excluding Long-term Committment [Line Items]
Intangible assets		13,800,000
License fees \| STMicro
Purchase Commitment, Excluding Long-term Committment [Line Items]
Payments to Acquire Intangible Assets	$ 17,000,000
Payments to Acquire Intangible Assets, Remainder of Calendar Year	10,100,000
Payments to Acquire Intangible Assets, Calendar Year Two	6,700,000
Payments to Acquire Intangible Assets, Calendar Year Three	$ 200,000
Intangible assets		9,800,000
Indemnification Agreement
Purchase Commitment, Excluding Long-term Committment [Line Items]
Indemnifications accrual		$ 0		$ 0

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

Commitments and Contingencies - Other Investments (Details)	1 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2017 CNY (¥)	Dec. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	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		¥ 243,800,000	$ 37,000,000
Total price payable under EPC Contract						¥ 540,000,000	$ 78,000,000
Contractual Obligation, Due in Second Calendar Year		¥ 296,200,000		$ 44,900,000
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