Document And Entity Information (USD $)	12 Months Ended
	Mar. 30, 2013	May 31, 2013	Sep. 29, 2012
Document And Entity Information [Abstract]
Entity Registrant Name	Supertex Inc
Entity Central Index Key	0000730000
Current Fiscal Year End Date	--03-30
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		11,535,836
Entity Public Float			$ 176,534,586
Entity Well-known Seasoned Issuer	No
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Mar. 30, 2013
Trading Symbol	supx