Document And Entity Information (USD $)	9 Months Ended
	Dec. 31, 2011	Feb. 03, 2012	Oct. 01, 2010
Entity Registrant Name	SUPERTEX INC
Entity Central Index Key	0000730000
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	No
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 247,183,092
Entity Common Stock, Shares Outstanding		12,061,218
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	Q3
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2011