-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 RPSIQD0Cd4yErNnvj0YquF5sCflkZvTIk4LDgOb76Z3kJz+RXcUpEFzCL1B92IPD
 hOVGfjWLU5peazTPgp0N5A==

<SEC-DOCUMENT>0001197204-03-000003.txt : 20030724
<SEC-HEADER>0001197204-03-000003.hdr.sgml : 20030724
<ACCEPTANCE-DATETIME>20030724143803
ACCESSION NUMBER:		0001197204-03-000003
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030722
FILED AS OF DATE:		20030724

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			SCHIE DAVID
		CENTRAL INDEX KEY:			0001197204

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-12718
		FILM NUMBER:		03800731

	BUSINESS ADDRESS:	
		STREET 1:		1235 BORDEAUX DRIVE
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SUPERTEX INC
		CENTRAL INDEX KEY:			0000730000
		STANDARD INDUSTRIAL CLASSIFICATION:	SEMICONDUCTORS & RELATED DEVICES [3674]
		IRS NUMBER:				942328535
		STATE OF INCORPORATION:			CA
		FISCAL YEAR END:			0331

	BUSINESS ADDRESS:	
		STREET 1:		1235 BORDEAUX DR
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089
		BUSINESS PHONE:		4087440100

	MAIL ADDRESS:	
		STREET 1:		1235 BORDEAUX DR
		CITY:			SUNNYVALE
		STATE:			CA
		ZIP:			94089
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-07-22</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000730000</issuerCik>
        <issuerName>SUPERTEX INC</issuerName>
        <issuerTradingSymbol>SUPX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001197204</rptOwnerCik>
            <rptOwnerName>SCHIE DAVID</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>V.P. Telecom and Broadband</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-07-22</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>S</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>300</value>
            </transactionShares>
            <transactionValue>
                <value>18.17</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>468</value>
                <footnoteId id="F1"/>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-07-22</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>S</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>468</value>
            </transactionShares>
            <transactionValue>
                <value>18.16</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>D</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>0</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <footnotes>
        <footnote id="F1">Other Grants: NQ Option (to purchase common stock).  Exercise Price $28.3125.  Shares granted: 60,000.  Shares exercisable currently: 36,000.  12,000 shares exercisable on 6/1/2004.  12,000 shares exercisable on 6/1/2005.  Expiration date: 6/1/2007.  Held direct.</footnote>
        <footnote id="F2">Other Grants:  ISO Option (to purchase common stock).  Exercise price $12.5300.  Shares granted: 7,980.  7,980 shares exercisable on 6/1/2006.  Expiration date: 6/1/2008.  Held direct.</footnote>
        <footnote id="F3">Other Grants:  NQ Option (to purchase common stock).  Exercise price: $12.5300.  Shares granted: 4,020.  4,020 shares exercisable on 6/1/2006.  Expiration date: 6/1/2008.  Held direct.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>David Schie</signatureName>
        <signatureDate>2003-07-24</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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