-----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,
 LYyWoGTm8SVG3ETd8QOzuUBf0UujeoeI3pOh0NevD4ALgaf6YBYabgKCtWZWukLK
 PPL9+Salr6C/GM3R2g4QWw==

<SEC-DOCUMENT>0001246153-04-000022.txt : 20040223
<SEC-HEADER>0001246153-04-000022.hdr.sgml : 20040223
<ACCEPTANCE-DATETIME>20040223180757
ACCESSION NUMBER:		0001246153-04-000022
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20040219
FILED AS OF DATE:		20040223

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			SIEBEL SYSTEMS INC
		CENTRAL INDEX KEY:			0001006835
		STANDARD INDUSTRIAL CLASSIFICATION:	SERVICES-PREPACKAGED SOFTWARE [7372]
		IRS NUMBER:				943187233
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404
		BUSINESS PHONE:		6504775000

	MAIL ADDRESS:	
		STREET 1:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			HOUSE PATRICIA A
		CENTRAL INDEX KEY:			0001241633

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	000-20725
		FILM NUMBER:		04623047

	BUSINESS ADDRESS:	
		STREET 1:		C/O SIEBEL SYSTEMS INC
		STREET 2:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404
		BUSINESS PHONE:		6504775000

	MAIL ADDRESS:	
		STREET 1:		C/O SIEBEL SYSTEMS INC
		STREET 2:		2207 BRIDGEPOINTE PARKWAY
		CITY:			SAN MATEO
		STATE:			CA
		ZIP:			94404
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>c0001241633d20040223f4f.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0201</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2004-02-19</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001006835</issuerCik>
        <issuerName>SIEBEL SYSTEMS INC</issuerName>
        <issuerTradingSymbol>SEBL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001241633</rptOwnerCik>
            <rptOwnerName>HOUSE PATRICIA A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SIEBEL SYSTEMS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>2207 BRIDGEPOINTE PARKWAY</rptOwnerStreet2>
            <rptOwnerCity>SAN MATEO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94404</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Vice Chairman and Co-Founder</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2004-02-19</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>65000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>14.02</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>966228</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>89364</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>Patricia A. House Separate Property Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Reporting person acquired 461 shares of Common Stock on June 30, 2003 at $6.29 per share through the company's Employee Stock Purchase Plan.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Patricia A House</signatureName>
        <signatureDate>2004-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>

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