Document And Entity Information	9 Months Ended
	Dec. 29, 2012	Feb. 01, 2013
Document And Entity Information [Abstract]
Entity Registrant Name	Supertex Inc
Entity Central Index Key	0000730000
Current Fiscal Year End Date	--03-30
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Well-known Seasoned Issuer	No
Entity Filer Category	Accelerated Filer
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 29, 2012
Trading Symbol	supx
Entity Common Stock, Shares Outstanding		11,514,950