Document and Entity Information	3 Months Ended
	Sep. 30, 2011	Oct. 31, 2011
Entity Information [Line Items]
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	Sep. 30, 2011
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		24,444,340