Document And Entity Information	3 Months Ended
	Jun. 30, 2012	Aug. 03, 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
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2012
Trading Symbol	supx
Entity Common Stock, Shares Outstanding		11,800,306