<PAGE>   1
     As filed with the Securities and Exchange Commission on July 11, 1996,
                                                      Registration No. 333-
- --------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                            -----------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                            -----------------------

                              SIEBEL SYSTEMS, INC.
             (Exact name of registrant as specified in its charter)

      Delaware                                            94-3187233
State of Incorporation                        I.R.S. Employer Identification No.

                            -----------------------

                               4005 Bohannon Drive
                          Menlo Park, California 94025
                                 (415) 329-6500
          (Address and telephone number of principal executive offices)

                            -----------------------

                           1996 Equity Incentive Plan
                          Employee Stock Purchase Plan
                            (Full title of the plans)

                                Thomas M. Siebel
                 Chairman, Chief Executive Officer and President
                               4005 Bohannon Drive
                          Menlo Park, California 94025
                                 (415) 329-6500
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                            -----------------------

                                   Copies to:
                              Eric C. Jensen, Esq.
                     Cooley Godward Castro Huddleson & Tatum
                     3000 Sand Hill Road, Bldg. 3, Suite 230
                          Menlo Park, California 94025
                                 (415) 843-5000

                            -----------------------
<PAGE>   2
                         CALCULATION OF REGISTRATION FEE

<TABLE>
================================================================================================
<CAPTION>
================================================================================================
                                        PROPOSED MAXIMUM     PROPOSED MAXIMUM
TITLE OF SECURITIES    AMOUNT TO BE    OFFERING PRICE PER   AGGREGATE OFFERING      AMOUNT OF
 TO BE REGISTERED       REGISTERED          SHARE(1)             PRICE(1)       REGISTRATION FEE
- ------------------------------------------------------------------------------------------------
<S>                    <C>             <C>                   <C>                <C>
Stock Options and
Common Stock (par
  value $.001)          5,483,790       $4.21 & $28.375     $49,205,254.50      $16,968.00
================================================================================================
</TABLE>



(1)      Estimated solely for the purpose of calculating the amount of the
         registration fee pursuant to Rule 457(h). The price per share and
         aggregate offering price are based upon the average of the high and low
         prices of Registrant's Common Stock on July 8, 1996 as reported on
         the Nasdaq National Market.

================================================================================
         The chart below details the calculations of the registration fee.

<TABLE>
<CAPTION>
===================================================================================
                                 NUMBER OF      OFFERING PRICE        AGGREGATE
SECURITIES                        SHARES           PER SHARE        OFFERING PRICE
- -----------------------------------------------------------------------------------
<S>                             <C>               <C>              <C>
Shares issuable pursuant to    
outstanding options under
the 1996 Equity Incentive
Plan                            4,402,950         $4.21            $18,536,419.50
- -----------------------------------------------------------------------------------
Shares available for                                     
additional grants under the                              
1996 Equity Incentive Plan        730,840         $28.375          $20,737,585
- -----------------------------------------------------------------------------------
Shares issuable pursuant to                              
the Employee Stock                                       
Purchase Plan                     350,000         $28.375          $ 9,931,250
- -----------------------------------------------------------------------------------
Proposed Maximum                                    
Offering Price                                                     $49,205,254.50
- -----------------------------------------------------------------------------------
                                                                  x .000344827
- -----------------------------------------------------------------------------------
Registration Fee                                                    $16,968.00
===================================================================================
</TABLE>

         Approximate date of commencement of proposed sale to the public: As
soon as practicable after this Registration Statement becomes effective.

<PAGE>   3
                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

         The following documents filed by Siebel Systems, Inc. (the
"Registrant") with the Securities and Exchange Commission (the "Commission") are
incorporated by reference into this Registration Statement:

         (a) The Registrant's latest prospectus filed pursuant to Rule 424(b)
under the Securities Act of 1933, as amended (the "Securities Act"), that
contains audited financial statements for the Registrant's latest fiscal year
for which such statements have been filed.

         (b) All other reports filed pursuant to Sections 13(a) or 15(d) of
Securities Exchange Act of 1934, as amended (the "Exchange Act"), since the end
of the fiscal year covered by the annual reports, the prospectus or the
registration statement referred to in (a) above.

         (c) The description of the Registrant's Common Stock ("Common Stock")
which is contained in the Registration Statement Form 8-A filed under the
Exchange Act, including any amendment or report filed for the purpose of
updating such description.

         All reports and other documents subsequently filed by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the
filing of a post-effective amendment, which indicates that all securities
offered have been sold or which deregisters all securities then remaining
unsold, shall be deemed to be incorporated by reference herein and to be a part
of this Registration Statement from the date of the filing of such reports and
documents.

                            DESCRIPTION OF SECURITIES

         Not Applicable.

                     INTERESTS OF NAMED EXPERTS AND COUNSEL

         As of July 10, 1996, attorneys affiliated with Cooley Godward Castro
Huddleson & Tatum ("Cooley Godward") beneficially owned through an investment
partnership an aggregate of 28,000 shares of Common Stock and James C. Gaither,
a director of the Company and a partner of Cooley Godward, owned 88,000 shares
of Common Stock and has an option to purchase 22,000 shares of Common Stock.

                    INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The Registrant's Bylaws provide that the Registrant will indemnify its
directors and executive officers and may indemnify its other officers, employees
and other agents to the fullest extent permitted by Delaware law. The Registrant
is also empowered under its Bylaws to enter into indemnification contracts with
its directors and officers and to purchase insurance on behalf of any person it
is required or permitted to indemnify. Pursuant to this provision, the
Registrant has entered into indemnity agreements with each of its directors and
executive officers.

         In addition, the Registrant's Certificate of Incorporation provides
that, to the fullest extent permitted by Delaware law, the Registrant's
directors will not be liable for monetary damages for breach of the directors'
fiduciary duty of care to the Registrant and its stockholders. This provision in
the Certificate of Incorporation does not eliminate the duty of care, and, in
appropriate circumstances, equitable remedies such as an injunction or other
forms of non-monetary relief would remain available under Delaware law. Each
director will continue to be subject to liability for breach of director's duty
of loyalty to the Registrant, for acts or omissions not in good faith or
involving intentional misconduct, for knowing violation of the law, for any
transaction from which the director derived an improper personal benefit, for
improper transactions between the director and the Registrant, and for improper
distribution to stockholders and loans to directors and officers. This provision
also does not affect a

                                       1.
<PAGE>   4
director's responsibilities under any other laws, such as federal and state 
securities laws or state and federal environmental laws.

                       EXEMPTION FROM REGISTRATION CLAIMED

         Not Applicable.

                                    EXHIBITS

EXHIBIT
NUMBER

(1)4.1          Restated Certificate of Incorporation of the Registrant

(1)4.2          Bylaws of the Registrant

(1)4.3          Specimen Stock Certificate

(1)4.4          Restated Investor Rights Agreement, dated December 1, 1995,
                between the Registrant and certain investors, as amended April
                30, 1996

(1)4.5          Amendment Number 2 to the Amended and Restated Investor Rights
                Agreement dated June 14, 1996

5.1             Opinion of Cooley Godward Castro Huddleson & Tatum

23.1            Consent of KPMG Peat Marwick LLP, Independent Auditors

23.2            Consent of Cooley Godward Castro Huddleson & Tatum is contained
                in Exhibit 5 to this Registration Statement

24.1            Power of Attorney is contained on the signature pages

(1)99.1         1996 Equity Incentive Plan

(1)99.2         Form of Nonstatutory Stock Option

(1)99.3         Form of Incentive Stock Option

(1)99.4         Employee Stock Purchase Plan

- --------------------
(1)    Filed as an exhibit to the Registrant's Registration Statement on Form
       S-1 (No. 333-03751), as amended through the date hereof, and incorporated
       herein by reference.


                                       2.
<PAGE>   5
                                  UNDERTAKINGS

      1. The undersigned Registrant hereby undertakes:

         (a)    To file, during any period in which offers or sales are being 
made, a post-effective amendment to this Registration Statement:

                (i) To include any prospectus required by section 10(a)(3) of
the Securities Act;

                (ii) To reflect in the prospectus any facts or events arising
after the effective date of the Registration Statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate,
represent a fundamental change in the information set forth in the Registration
Statement. Notwithstanding the foregoing, any increase or decrease in volume of
securities offered (if the total dollar value of securities offered would not
exceed that which was registered) and any deviation from the low or high end of
the estimated maximum offering range may be reflected in the form of prospectus
filed with the Commission pursuant to Rule 424(b) (Section 230.424(b) of this
chapter) if, in the aggregate, the changes in volume and price represent no more
than a 20% change in the maximum aggregate offering price set forth in the
"Calculation of Registration Fee" table in the effective Registration Statement.

                (iii) To include any material information with respect to the
plan of distribution not previously disclosed in the Registration Statement or
any material change to such information in the Registration Statement;

         Provided, however, that paragraphs (1)(a)(i) and (1)(a)(ii) do not
apply if the Registration Statement is on Form S-3, Form S-8 or Form F-3, and
the information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the Registrant pursuant to Section 13 or Section 15(d) of the
Exchange Act that are incorporated by reference in the Registration Statement.

         (b)    That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
Registration Statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

         (c)    To remove from registration by means of a post-effective 
amendment any of the securities being registered which remain unsold at the
termination of the offering.

      2. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new Registration Statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

      3. Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Commission such indemnification is
against public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such


                                       3.
<PAGE>   6
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.













































                                       4.
<PAGE>   7
                                   SIGNATURES

        Pursuant to the requirements of the Securities Act  the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Menlo Park, State of California, on July 10, 1996.

                                      SIEBEL SYSTEMS, INC.



                                      By:    /s/ Thomas M. Siebel
                                          --------------------------------
                                             Thomas M.Siebel
                                             Chairman, President
                                             and Chief Executive Officer


                                POWER OF ATTORNEY

      KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Thomas M. Siebel and Justin R. Dooley,
and each or any one of them, his true and lawful attorney-in-fact and agent,
with full power of substitution and resubstitution, for him and in his name,
place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite and necessary to be done in
connection therewith, as fully to all intents and purposes as he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents, or any of them, or their or his substitutes or substitute, may
lawfully do or cause to be done by virtue hereof.


                                       5.
<PAGE>   8
      Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.


<TABLE>
<CAPTION>
SIGNATURE                               TITLE                                   DATE
<S>                                     <C>                                     <C>
    /s/ Thomas M. Siebel                President, Chief Executive Officer      July 10, 1996
- ---------------------------------       and Chairman of the Board               
     (Thomas M. Siebel)                 (Principal Executive Officer)     
 
                                                                     

      /s/ Justin R. Dooley              Vice President Finance and              July 10, 1996 
- ---------------------------------       Administration (Principal Financial     
       (Justin R. Dooley)               and Accounting Officer)            

                                       
                                        

        /s/ Pehong Chen                 Director                                July 10, 1996    
- ---------------------------------
         (Pehong Chen)                                                          
                                        
 
       /s/ James C. Gaither             Director                                July 10, 1996     
- ---------------------------------
        (James C. Gaither)                                                     
                                        

        /s/ Eric E. Schmidt             Director                                July 10, 1996     
- ---------------------------------
         (Eric E. Schmidt)                                                      
                                        
 
       /s/ Charles R. Schwab            Director                                July 10, 1996      
- ---------------------------------
        (Charles R. Schwab)                                                    
                                        

       /s/ George T. Shaheen            Director                                July 10, 1996      
- ---------------------------------
        (George T. Shaheen)                                                    
                                        

       /s/ A. Michael Spence            Director                                July 10, 1996   
- ---------------------------------
        (A. Michael Spence)                                                    
                                        

</TABLE>


                                       6.


<PAGE>   9
                                  EXHIBIT INDEX

EXHIBIT
NUMBER

(1)4.1      Restated Certificate of Incorporation of the Registrant

(1)4.2      Bylaws of the Registrant

(1)4.3      Specimen Stock Certificate

(1)4.4      Restated Investor Rights Agreement, dated December 1, 1995, between
            the Registrant and certain investors, as amended April 30, 1996

(1)4.5      Amendment Number 2 to the Amended and Restated Investor Rights
            Agreement dated June 14, 1996

5.1         Opinion of Cooley Godward Castro Huddleson & Tatum

23.1        Consent of KPMG Peat Marwick LLP, Independent Auditors

23.2        Consent of Cooley Godward Castro Huddleson & Tatum is contained in
            Exhibit 5 to this Registration Statement

24.1        Power of Attorney is contained on the signature pages

(1)99.1     1996 Equity Incentive Plan

(1)99.2     Form of Nonstatutory Stock Option

(1)99.3     Form of Incentive Stock Option

(1)99.4     Employee Stock Purchase Plan



- ----------------------------

(1)  Filed as an exhibit to the Registrant's Registration Statement on Form S-1
     (No. 333-03751), as amended through the date hereof, and incorporated
     herein by reference.




                                       7.
[{"type": "S-8", "sequence": "1", "description": "FORM S-8", "secsgml_size_bytes": 21324}]
{"company-data": {"conformed-name": "SIEBEL SYSTEMS INC", "cik": "0001006835", "assigned-sic": "7372", "irs-number": "943187233", "state-of-incorporation": "DE", "fiscal-year-end": "1231"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-07983", "film-number": "96593659"}, "business-address": {"street1": "4005 BOHANNON DR", "city": "MENLO PARK", "state": "CA", "zip": "94025", "phone": "4153296500"}, "mail-address": {"street1": "4005 BOHANNON DR", "city": "MENLO PARK", "state": "CA", "zip": "94025"}}
1
     As filed with the Securities and Exchange Commission on July 11, 1996,
                                                      Registration No. 333-
- --------------------------------------------------------------------------------

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                            -----------------------

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

                            -----------------------

                              SIEBEL SYSTEMS, INC.
             (Exact name of registrant as specified in its charter)

      Delaware                                            94-3187233
State of Incorporation                        I.R.S. Employer Identification No.

                            -----------------------

                               4005 Bohannon Drive
                          Menlo Park, California 94025
                                 (415) 329-6500
          (Address and telephone number of principal executive offices)

                            -----------------------

                           1996 Equity Incentive Plan
                          Employee Stock Purchase Plan
                            (Full title of the plans)

                                Thomas M. Siebel
                 Chairman, Chief Executive Officer and President
                               4005 Bohannon Drive
                          Menlo Park, California 94025
                                 (415) 329-6500
 (Name, address, including zip code, and telephone number, including area code,
                             of agent for service)

                            -----------------------

                                   Copies to:
                              Eric C. Jensen, Esq.
                     Cooley Godward Castro Huddleson & Tatum
                     3000 Sand Hill Road, Bldg. 3, Suite 230
                          Menlo Park, California 94025
                                 (415) 843-5000

                            -----------------------
2
                         CALCULATION OF REGISTRATION FEE

================================================================================================
================================================================================================
                                        PROPOSED MAXIMUM     PROPOSED MAXIMUM
TITLE OF SECURITIES    AMOUNT TO BE    OFFERING PRICE PER   AGGREGATE OFFERING      AMOUNT OF
 TO BE REGISTERED       REGISTERED          SHARE(1)             PRICE(1)       REGISTRATION FEE
- ------------------------------------------------------------------------------------------------
Stock Options and
Common Stock (par
  value $.001)          5,483,790       $4.21 & $28.375     $49,205,254.50      $16,968.00
================================================================================================
(1)      Estimated solely for the purpose of calculating the amount of the
         registration fee pursuant to Rule 457(h). The price per share and
         aggregate offering price are based upon the average of the high and low
         prices of Registrant's Common Stock on July 8, 1996 as reported on
         the Nasdaq National Market.

================================================================================
         The chart below details the calculations of the registration fee.
===================================================================================
                                 NUMBER OF      OFFERING PRICE        AGGREGATE
SECURITIES                        SHARES           PER SHARE        OFFERING PRICE
- -----------------------------------------------------------------------------------
Shares issuable pursuant to    
outstanding options under
the 1996 Equity Incentive
Plan                            4,402,950         $4.21            $18,536,419.50
- -----------------------------------------------------------------------------------
Shares available for                                     
additional grants under the                              
1996 Equity Incentive Plan        730,840         $28.375          $20,737,585
- -----------------------------------------------------------------------------------
Shares issuable pursuant to                              
the Employee Stock                                       
Purchase Plan                     350,000         $28.375          $ 9,931,250
- -----------------------------------------------------------------------------------
Proposed Maximum                                    
Offering Price                                                     $49,205,254.50
- -----------------------------------------------------------------------------------
                                                                  x .000344827
- -----------------------------------------------------------------------------------
Registration Fee                                                    $16,968.00
===================================================================================
Approximate date of commencement of proposed sale to the public: As
soon as practicable after this Registration Statement becomes effective.
3
                 INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

         The following documents filed by Siebel Systems, Inc. (the
"Registrant") with the Securities and Exchange Commission (the "Commission") are
incorporated by reference into this Registration Statement:

         (a) The Registrant's latest prospectus filed pursuant to Rule 424(b)
under the Securities Act of 1933, as amended (the "Securities Act"), that
contains audited financial statements for the Registrant's latest fiscal year
for which such statements have been filed.

         (b) All other reports filed pursuant to Sections 13(a) or 15(d) of
Securities Exchange Act of 1934, as amended (the "Exchange Act"), since the end
of the fiscal year covered by the annual reports, the prospectus or the
registration statement referred to in (a) above.

         (c) The description of the Registrant's Common Stock ("Common Stock")
which is contained in the Registration Statement Form 8-A filed under the
Exchange Act, including any amendment or report filed for the purpose of
updating such description.

         All reports and other documents subsequently filed by the Registrant
pursuant to Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act prior to the
filing of a post-effective amendment, which indicates that all securities
offered have been sold or which deregisters all securities then remaining
unsold, shall be deemed to be incorporated by reference herein and to be a part
of this Registration Statement from the date of the filing of such reports and
documents.

                            DESCRIPTION OF SECURITIES

         Not Applicable.

                     INTERESTS OF NAMED EXPERTS AND COUNSEL

         As of July 10, 1996, attorneys affiliated with Cooley Godward Castro
Huddleson & Tatum ("Cooley Godward") beneficially owned through an investment
partnership an aggregate of 28,000 shares of Common Stock and James C. Gaither,
a director of the Company and a partner of Cooley Godward, owned 88,000 shares
of Common Stock and has an option to purchase 22,000 shares of Common Stock.

                    INDEMNIFICATION OF DIRECTORS AND OFFICERS

         The Registrant's Bylaws provide that the Registrant will indemnify its
directors and executive officers and may indemnify its other officers, employees
and other agents to the fullest extent permitted by Delaware law. The Registrant
is also empowered under its Bylaws to enter into indemnification contracts with
its directors and officers and to purchase insurance on behalf of any person it
is required or permitted to indemnify. Pursuant to this provision, the
Registrant has entered into indemnity agreements with each of its directors and
executive officers.

         In addition, the Registrant's Certificate of Incorporation provides
that, to the fullest extent permitted by Delaware law, the Registrant's
directors will not be liable for monetary damages for breach of the directors'
fiduciary duty of care to the Registrant and its stockholders. This provision in
the Certificate of Incorporation does not eliminate the duty of care, and, in
appropriate circumstances, equitable remedies such as an injunction or other
forms of non-monetary relief would remain available under Delaware law. Each
director will continue to be subject to liability for breach of director's duty
of loyalty to the Registrant, for acts or omissions not in good faith or
involving intentional misconduct, for knowing violation of the law, for any
transaction from which the director derived an improper personal benefit, for
improper transactions between the director and the Registrant, and for improper
distribution to stockholders and loans to directors and officers. This provision
also does not affect a

                                       1.
4
director's responsibilities under any other laws, such as federal and state 
securities laws or state and federal environmental laws.

                       EXEMPTION FROM REGISTRATION CLAIMED

         Not Applicable.

                                    EXHIBITS

EXHIBIT
NUMBER

(1)4.1          Restated Certificate of Incorporation of the Registrant

(1)4.2          Bylaws of the Registrant

(1)4.3          Specimen Stock Certificate

(1)4.4          Restated Investor Rights Agreement, dated December 1, 1995,
                between the Registrant and certain investors, as amended April
                30, 1996

(1)4.5          Amendment Number 2 to the Amended and Restated Investor Rights
                Agreement dated June 14, 1996

5.1             Opinion of Cooley Godward Castro Huddleson & Tatum

23.1            Consent of KPMG Peat Marwick LLP, Independent Auditors

23.2            Consent of Cooley Godward Castro Huddleson & Tatum is contained
                in Exhibit 5 to this Registration Statement

24.1            Power of Attorney is contained on the signature pages

(1)99.1         1996 Equity Incentive Plan

(1)99.2         Form of Nonstatutory Stock Option

(1)99.3         Form of Incentive Stock Option

(1)99.4         Employee Stock Purchase Plan

- --------------------
(1)    Filed as an exhibit to the Registrant's Registration Statement on Form
       S-1 (No. 333-03751), as amended through the date hereof, and incorporated
       herein by reference.

                                       2.
5
                                  UNDERTAKINGS

      1. The undersigned Registrant hereby undertakes:

         (a)    To file, during any period in which offers or sales are being 
made, a post-effective amendment to this Registration Statement:

                (i) To include any prospectus required by section 10(a)(3) of
the Securities Act;

                (ii) To reflect in the prospectus any facts or events arising
after the effective date of the Registration Statement (or the most recent
post-effective amendment thereof) which, individually or in the aggregate,
represent a fundamental change in the information set forth in the Registration
Statement. Notwithstanding the foregoing, any increase or decrease in volume of
securities offered (if the total dollar value of securities offered would not
exceed that which was registered) and any deviation from the low or high end of
the estimated maximum offering range may be reflected in the form of prospectus
filed with the Commission pursuant to Rule 424(b) (Section 230.424(b) of this
chapter) if, in the aggregate, the changes in volume and price represent no more
than a 20% change in the maximum aggregate offering price set forth in the
"Calculation of Registration Fee" table in the effective Registration Statement.

                (iii) To include any material information with respect to the
plan of distribution not previously disclosed in the Registration Statement or
any material change to such information in the Registration Statement;

         Provided, however, that paragraphs (1)(a)(i) and (1)(a)(ii) do not
apply if the Registration Statement is on Form S-3, Form S-8 or Form F-3, and
the information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed with or furnished to the
Commission by the Registrant pursuant to Section 13 or Section 15(d) of the
Exchange Act that are incorporated by reference in the Registration Statement.

         (b)    That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
Registration Statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

         (c)    To remove from registration by means of a post-effective 
amendment any of the securities being registered which remain unsold at the
termination of the offering.

      2. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new Registration Statement relating to the securities offered herein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

      3. Insofar as indemnification for liabilities arising under the Securities
Act may be permitted to directors, officers and controlling persons of the
Registrant pursuant to the foregoing provisions, or otherwise, the Registrant
has been advised that in the opinion of the Commission such indemnification is
against public policy as expressed in the Securities Act and is, therefore,
unenforceable. In the event that a claim for indemnification against such
liabilities (other than the payment by the Registrant of expenses incurred or
paid by a director, officer or controlling person of the Registrant in the
successful defense of any action, suit or proceeding) is asserted by such

                                       3.
6
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

                                       4.
7
                                   SIGNATURES

        Pursuant to the requirements of the Securities Act  the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Menlo Park, State of California, on July 10, 1996.

                                      SIEBEL SYSTEMS, INC.

                                      By:    /s/ Thomas M. Siebel
                                          --------------------------------
                                             Thomas M.Siebel
                                             Chairman, President
                                             and Chief Executive Officer

                                POWER OF ATTORNEY

      KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Thomas M. Siebel and Justin R. Dooley,
and each or any one of them, his true and lawful attorney-in-fact and agent,
with full power of substitution and resubstitution, for him and in his name,
place and stead, in any and all capacities, to sign any and all amendments
(including post-effective amendments) to this Registration Statement, and to
file the same, with all exhibits thereto, and other documents in connection
therewith, with the Securities and Exchange Commission, granting unto said
attorneys-in-fact and agents, and each of them, full power and authority to do
and perform each and every act and thing requisite and necessary to be done in
connection therewith, as fully to all intents and purposes as he might or could
do in person, hereby ratifying and confirming all that said attorneys-in-fact
and agents, or any of them, or their or his substitutes or substitute, may
lawfully do or cause to be done by virtue hereof.

                                       5.
8
      Pursuant to the requirements of the Securities Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.
SIGNATURE                               TITLE                                   DATE
/s/ Thomas M. Siebel                President, Chief Executive Officer      July 10, 1996
- ---------------------------------       and Chairman of the Board               
     (Thomas M. Siebel)                 (Principal Executive Officer)     
 
                                                                     

      /s/ Justin R. Dooley              Vice President Finance and              July 10, 1996 
- ---------------------------------       Administration (Principal Financial     
       (Justin R. Dooley)               and Accounting Officer)            

                                       
                                        

        /s/ Pehong Chen                 Director                                July 10, 1996    
- ---------------------------------
         (Pehong Chen)                                                          
                                        
 
       /s/ James C. Gaither             Director                                July 10, 1996     
- ---------------------------------
        (James C. Gaither)                                                     
                                        

        /s/ Eric E. Schmidt             Director                                July 10, 1996     
- ---------------------------------
         (Eric E. Schmidt)                                                      
                                        
 
       /s/ Charles R. Schwab            Director                                July 10, 1996      
- ---------------------------------
        (Charles R. Schwab)                                                    
                                        

       /s/ George T. Shaheen            Director                                July 10, 1996      
- ---------------------------------
        (George T. Shaheen)                                                    
                                        

       /s/ A. Michael Spence            Director                                July 10, 1996   
- ---------------------------------
        (A. Michael Spence)
6.
9
                                  EXHIBIT INDEX

EXHIBIT
NUMBER

(1)4.1      Restated Certificate of Incorporation of the Registrant

(1)4.2      Bylaws of the Registrant

(1)4.3      Specimen Stock Certificate

(1)4.4      Restated Investor Rights Agreement, dated December 1, 1995, between
            the Registrant and certain investors, as amended April 30, 1996

(1)4.5      Amendment Number 2 to the Amended and Restated Investor Rights
            Agreement dated June 14, 1996

5.1         Opinion of Cooley Godward Castro Huddleson & Tatum

23.1        Consent of KPMG Peat Marwick LLP, Independent Auditors

23.2        Consent of Cooley Godward Castro Huddleson & Tatum is contained in
            Exhibit 5 to this Registration Statement

24.1        Power of Attorney is contained on the signature pages

(1)99.1     1996 Equity Incentive Plan

(1)99.2     Form of Nonstatutory Stock Option

(1)99.3     Form of Incentive Stock Option

(1)99.4     Employee Stock Purchase Plan

- ----------------------------

(1)  Filed as an exhibit to the Registrant's Registration Statement on Form S-1
     (No. 333-03751), as amended through the date hereof, and incorporated
     herein by reference.

                                       7.