-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 VyNWGLVFXrNSkacFUb3wgQgFOtLC9ObyomWInSgrFlEKENexRSn8E9kCy+KI1xpW
 zxBmo3e/jxvS1V3qBW5Y6Q==

<SEC-DOCUMENT>0001140361-10-022464.txt : 20100520
<SEC-HEADER>0001140361-10-022464.hdr.sgml : 20100520
<ACCEPTANCE-DATETIME>20100520183621
ACCESSION NUMBER:		0001140361-10-022464
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100518
FILED AS OF DATE:		20100520
DATE AS OF CHANGE:		20100520

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Caulfield Thomas
		CENTRAL INDEX KEY:			0001342570

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-31311
		FILM NUMBER:		10848995

	MAIL ADDRESS:	
		STREET 1:		4000 NORTH FIRST STREET
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95134

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			PDF SOLUTIONS INC
		CENTRAL INDEX KEY:			0001120914
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-COMPUTER PROGRAMMING SERVICES [7371]
		IRS NUMBER:				251701361
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		333 WEST SAN CARLOS STREET
		STREET 2:		SUITE 700
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95110
		BUSINESS PHONE:		4082807900

	MAIL ADDRESS:	
		STREET 1:		333 WEST SAN JOSE STREET
		STREET 2:		SUITE 700
		CITY:			SAN JOSE
		STATE:			CA
		ZIP:			95110
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-05-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001120914</issuerCik>
        <issuerName>PDF SOLUTIONS INC</issuerName>
        <issuerTradingSymbol>PDFS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001342570</rptOwnerCik>
            <rptOwnerName>Caulfield Thomas</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>333 WEST SAN CARLOS ST</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 700</rptOwnerStreet2>
            <rptOwnerCity>SAN JOSE</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>95110</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>2001 Stock Plan Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>4.82</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-05-18</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>22500</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-05-18</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-05-18</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>22500</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>22500</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">1/4th of the total number of shares will vest on May 18, 2011 and the reminder will vest in 36 equal monthly installments thereafter on the 18th of each month, provided that the reporting person continues to serve as a director on the Board of Directors.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Joy E. Leo, Attorney-in-Fact for Thomas Caulfield</signatureName>
        <signatureDate>2010-05-20</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
-----END PRIVACY-ENHANCED MESSAGE-----
