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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No. 7)*

Siebel Systems Inc.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

82617012

                                (CUSIP Number)                                

December 31, 2003

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

¨ Rule 13d-1(c)

x Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

Potential persons who are to respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

SEC 1745 (3-98)

CUSIP No. 826170102 13G Page 2 of 10 Pages

1.	Name of Reporting Person I.R.S. Identification No. of above person (entities only).             Thomas M. Siebel
2.	Check the Appropriate Box if a Member of a Group* (a)  ¨ (b)  ¨
3.	SEC Use Only
4.	Citizenship or Place of Organization             USA

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH   5.    Sole Voting Power                 57,348,475(1)   6.    Shared Voting Power                 -0-   7.    Sole Dispositive Power                 57,348,475(1)   8.    Shared Dispositive Power                 -0-

9.	Aggregate Amount Beneficially Owned by Each Reporting Person             57,348,475(1)
10.	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares* ¨
11.	Percent of Class Represented by Amount in Row 9             11.09%
12.	Type of Reporting Person*             IN

(1) Includes 32,249,752 shares held by Thomas M. Siebel, Trustee or Successor Trustee of the Siebel Living Trust u/a/d 7/27/93, 2,349,904 shares held by Siebel Asset Management L.P. and 1,635,840 shares held by Siebel Asset Management III L.P. Also includes 2,426,845 shares held by the Thomas and Stacey Siebel Foundation, of which the reporting person disclaims beneficial ownership. Also includes 18,686,134 shares issuable pursuant to options exercisable within 60 days of December 31, 2003.

*SEE INSTRUCTION BEFORE FILLING OUT!

CUSIP No. 826170102 13G Page 3 of 10 Pages

1.	Name of Reporting Person I.R.S. Identification No(s). of above person(s) (entities only)             Thomas M. Siebel, Trustee or Successor Trustee of the Siebel Living Trust u/a/d 7/27/93
2.	Check the Appropriate Box if a Member of a Group* (a)  ¨ (b)  ¨
3.	SEC Use Only
4.	Citizenship or Place of Organization             California

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH   5.    Sole Voting Power                 32,249,752   6.    Shared Voting Power                 -0-   7.    Sole Dispositive Power                 32,249,752   8.    Shared Dispositive Power                 -0-

9.	Aggregate Amount Beneficially Owned by Each Reporting Person             32,249,752
10.	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares* ¨
11.	Percent of Class Represented by Amount in Row 9             6.5%
12.	Type of Reporting Person*             OO

*SEE INSTRUCTION BEFORE FILLING OUT!

CUSIP No. 826170102 13G Page 4 of 10 Pages

1.	Name of Reporting Person I.R.S. Identification No(s). of above person(s) (entities only).             Siebel Asset Management, L.P.
2.	Check the Appropriate Box if a Member of a Group* (a)  ¨ (b)  ¨
3.	SEC Use Only
4.	Citizenship or Place of Organization             California

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH   5.    Sole Voting Power                 2,349,904   6.    Shared Voting Power                 -0-   7.    Sole Dispositive Power                 2,349,904   8.    Shared Dispositive Power                 -0-

9.	Aggregate Amount Beneficially Owned by Each Reporting Person             2,349,904
10.	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares* ¨
11.	Percent of Class Represented by Amount in Row 9             0.5%
12.	Type of Reporting Person*             PN

*SEE INSTRUCTION BEFORE FILLING OUT!

CUSIP No. 826170102 13G Page 5 of 10 Pages

1.	Name of Reporting Person I.R.S. Identification No(s). of above person (entities only)             Thomas and Stacey Siebel Foundation
2.	Check the Appropriate Box if a Member of a Group* (a)  ¨ (b)  ¨
3.	SEC Use Only
4.	Citizenship or Place of Organization             California

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH   5.    Sole Voting Power                 2,426,845   6.    Shared Voting Power                 -0-   7.    Sole Dispositive Power                 2,426,845   8.    Shared Dispositive Power                 -0-

9.	Aggregate Amount Beneficially Owned by Each Reporting Person             2,426,845
10.	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares* ¨
11.	Percent of Class Represented by Amount in Row 9             0.5%
12.	Type of Reporting Person*             PN

*SEE INSTRUCTION BEFORE FILLING OUT!

CUSIP No. 826170102 13G Page 5 of 10 Pages

1.	Name of Reporting Person I.R.S. Identification No(s). of above person(s) (entities only)             Siebel Asset Management III, L.P.
2.	Check the Appropriate Box if a Member of a Group* (a)  ¨ (b)  ¨
3.	SEC Use Only
4.	Citizenship or Place of Organization             California

NUMBER OF SHARES BENEFICIALLY OWNED BY EACH REPORTING PERSON WITH   5.    Sole Voting Power                 1,635,840   6.    Shared Voting Power                 -0-   7.    Sole Dispositive Power                 1,635,840   8.    Shared Dispositive Power                 -0-

9.	Aggregate Amount Beneficially Owned by Each Reporting Person             1,635,840
10.	Check Box if the Aggregate Amount in Row (9) Excludes Certain Shares* ¨
11.	Percent of Class Represented by Amount in Row 9             0.3%
12.	Type of Reporting Person*             PN

*SEE INSTRUCTION BEFORE FILLING OUT!

Item 1.	(a)	Name of Issuer Siebel Systems, Inc.
	(b)	Address of Issuer’s Principal Executive Offices 2207 Bridgepointe Parkway San Mateo, CA 94404
Item 2.	(a)	Name of Person Filing Thomas M. Siebel Thomas M. Siebel, Trustee or Successor Trustee of the Siebel Living Trust u/a/d 7/27/93 (“Trust”) Siebel Asset Management, L.P. (“SAM”) Siebel Asset Management III, L.P. (“SAM III”) Thomas and Stacey Siebel Foundation (“Foundation”)
	(b)	Address of Principal Business Office or, if none, Residence 2207 Bridgepointe Parkway San Mateo, CA 94404
	(c)	Citizenship Thomas M. Siebel                     USA Trust                                           California SAM                                           California Foundation                                California SAM III                                     California
	(d)	Title of Class of Securities Common Stock
	(e)	CUSIP Number:     826170102
Item 3.	If this statement is filed pursuant to §§240.13d-1(b), or 240.13d-2(b) or (c), check whether the person filing is a:
	Not Applicable

Page 7 of 10 pages

Item 4.	Ownership Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.
	(a)	Amount beneficially owned:
		Thomas M. Siebel Trust SAM Foundation SAM III		57,348,475* 32,249,752 2,349,904 2,426,845 1,635,840
	(b)	Percent of class:
		Thomas M. Siebel Trust SAM Foundation SAM III		10.6% 6.5% 0.5% 0.5% 0.3%
	(c)	Number of shares as to which such person has:
		(i)	Sole power to vote or to direct the vote:
		Thomas M. Siebel Trust SAM Foundation SAM III		57,348,475* 32,249,752 2,349,904 2,426,845 1,635,840
		(ii)	Shared power to vote or to direct the vote:
		Thomas M. Siebel Trust SAM Foundation SAM III		0 0 0 0 0

* Includes 32,249,752 shares held by Thomas M. Siebel, Trustee or Successor Trustee of the Siebel Living Trust u/a/d 7/27/93, 2,349,904 shares held by Siebel Asset Management L.P. and 1,635,840 shares held by Siebel Asset Management III L.P. Also includes 2,426,845 shares held by the Thomas and Stacey Siebel Foundation, of which the reporting person disclaims beneficial ownership. Also includes 18,686,134 shares issuable pursuant to options exercisable within 60 days of December 31, 2003.

Page 8 of 10 pages

		(iii)	Sole power to dispose or to direct the disposition of:
		Thomas M. Siebel Trust SAM Foundation SAM III		57,348,475* 32,249,752 2,349,904 2,426,845 1,635,840
		(iv)	Shared power to dispose or to direct the disposition of:
		Thomas M. Siebel Trust SAM Foundation SAM III		0 0 0 0 0
Item 5.	Ownership of Five Percent or Less of a Class If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following ¨.
Item 6.	Ownership of More than Five Percent on Behalf of Another Person Under certain circumstances set forth in the partnership agreements of SAM, SAM III and SAM IV (the “SAM Entities”), the general and/or limited partners of the SAM Entities have the right to receive dividends from, or proceeds from the sale of, the Common Stock of the Issuer beneficially owned by the SAM Entities.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company Not applicable
Item 8.	Identification and Classification of Members of the Group Not applicable
Item 9.	Notice of Dissolution of a Group Not applicable
Item 10.	Certification Not applicable

* Includes 32,249,752 shares held by Thomas M. Siebel, Trustee or Successor Trustee of the Siebel Living Trust u/a/d 7/27/93, 2,349,904 shares held by Siebel Asset Management L.P. and 1,635,840 shares held by Siebel Asset Management III L.P. Also includes 2,426,845 shares held by the Thomas and Stacey Siebel Foundation, of which the reporting person disclaims beneficial ownership. Also includes 18,686,134 shares issuable pursuant to options exercisable within 60 days of December 31, 2003.

Page 9 of 10 pages

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

    2-12-04         

Date

    /s/    Thomas M. Siebel        

Signature

THOMAS M. SIEBEL, TRUSTEE OR SUCCESSOR TRUSTEE OF THE SIEBEL LIVING TRUST U/A/D 7/27/93

    /s/    Thomas M. Siebel        

Thomas M. Siebel, Trustee

SIEBEL ASSET MANAGEMENT, L.P.

    /s/    Thomas M. Siebel        

Thomas M. Siebel, General Partner

THOMAS AND STACEY SIEBEL FOUNDATION

    /s/    Thomas M. Siebel        

Thomas M. Siebel, President

SIEBEL ASSET MANAGEMENT III, L.P.

    /s/    Thomas M. Siebel        

Thomas M. Siebel, General Partner

Page 10 of 10 pages