AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON JUNE 20, 1996     
 
                                                      REGISTRATION NO. 333-4370
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                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C. 20549
 
                               ----------------
                         
                      POST-EFFECTIVE AMENDMENT NO. 1     
                                      TO
                                   FORM S-1
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933
 
                               ----------------
 
                                THERMATRIX INC.
            (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)
 
                               ----------------
 
 
                                                            
           DELAWARE                           3569                    94-2958515
(STATE OR OTHER JURISDICTION OF   (PRIMARY STANDARD INDUSTRIAL     (I.R.S. EMPLOYER
INCORPORATION OR ORGANIZATION)     CLASSIFICATION CODE NUMBER)   IDENTIFICATION NUMBER)
 
                               ----------------
 
                                101 METRO DRIVE
                                   SUITE 248
                          SAN JOSE, CALIFORNIA 95110
                                (408) 453-0490
  (ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE, OF
                   REGISTRANT'S PRINCIPAL EXECUTIVE OFFICES)
 
                               ----------------
 
                               JOHN T. SCHOFIELD
                CHAIRMAN, PRESIDENT AND CHIEF EXECUTIVE OFFICER
                                THERMATRIX INC.
                          101 METRO DRIVE, SUITE 248
                          SAN JOSE, CALIFORNIA 95110
                                (408) 453-0490
(NAME, ADDRESS, INCLUDING ZIP CODE, AND TELEPHONE NUMBER, INCLUDING AREA CODE,
                             OF AGENT FOR SERVICE)
                                  COPIES TO:
 
       MICHAEL J. DANAHER, ESQ.                HOWARD L. SHECTER, ESQ.
   WILSON SONSINI GOODRICH & ROSATI          MORGAN, LEWIS & BOCKIUS LLP
       PROFESSIONAL CORPORATION                    101 PARK AVENUE
          650 PAGE MILL ROAD                  NEW YORK, NEW YORK 10178
      PALO ALTO, CALIFORNIA 94304                  (212) 309-6000
            (415) 493-9300
                               ----------------
   
  APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC: June 20,
1996.     
 
                               ----------------
 
  If any of the securities being registered on this form are to be offered on
a delayed or continuous basis pursuant to Rule 415 under the Securities Act of
1933, check the following box. [_]
  If this form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act of 1933, please check the
following box and list the Securities Act registration statement number of the
earlier effective registration statement for the same offering. [_]
  If this form is a post-effective amendment filed pursuant to Rule 462(c)
under the Securities Act, check the following box and list the Securities Act
registration statement number of the earlier effective registration statement
for the same offering. [_]
  If delivery of the prospectus is expected to be made pursuant to Rule 434,
please check the following box. [_]
 
                               ----------------
 
  THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT
SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY STATES THAT THIS
REGISTRATION STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH
SECTION 8(A) OF THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION STATEMENT
SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING PURSUANT TO SAID
SECTION 8(A), MAY DETERMINE.
 
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                                    PART II
 
                    INFORMATION NOT REQUIRED IN PROSPECTUS
 
ITEM 13. OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION
 
  The following table sets forth the costs and expenses, other than
underwriting discounts and commissions, payable by the Registrant in
connection with the sale of Common Stock being registered. All amounts are
estimates except the registration fee and the NASD filing fee.
 


                                                                         AMOUNT
                                                                         TO BE
                                                                          PAID
                                                                        --------
                                                                     
   Registration Fee.................................................... $ 11,104
   NASD Filing Fee.....................................................    3,720
   Nasdaq National Market listing fee..................................   37,000
   Printing and Engraving..............................................  100,000
   Legal Fees and Expenses.............................................  300,000
   Accounting Fees and Expenses........................................  175,000
   Blue Sky Fees and Expenses..........................................   15,000
   Directors and Officers Insurance....................................  100,000
   Transfer Agent Fees.................................................   10,000
   Miscellaneous.......................................................   48,176
                                                                        --------
     Total............................................................. $800,000
                                                                        ========

 
ITEM 14. INDEMNIFICATION OF DIRECTORS AND OFFICERS
 
  As permitted by Section 145 of the Delaware General Corporation Law, the
Registrant's Restated Certificate of Incorporation includes a provision that
eliminates the personal liability of its directors for monetary damages for
breach or alleged breach of their duty of care. In addition, as permitted by
Section 145 of the Delaware General Corporation Law, the Amended and Restated
Bylaws of the Registrant provide that: (i) the Registrant is required to
indemnify its directors and executive officers and persons serving in such
capacities in other business enterprises (including, for example, subsidiaries
of the Registrant) at the Registrant's request, to the fullest extent
permitted by Delaware law, including in those circumstances in which
indemnification would otherwise be discretionary; (ii) the Registrant may, in
its discretion, indemnify employees and agents in those circumstances where
indemnification is not required by law; (iii) the Registrant is required to
advance expenses, as incurred, to its directors and executive officers in
connection with defending a proceeding (except that it is not required to
advance expenses to a person against whom the Registrant brings a claim) for
breach of the duty of loyalty, failure to act in good faith, intentional
misconduct, knowing violation of law or deriving an improper personal benefit;
(iv) the rights conferred in the Amended and Restated Bylaws are not
exclusive, and the Registrant is authorized to enter into indemnification
agreements with its directors, executive officers and employees; and (v) the
Registrant may not retroactively amend the Bylaw provisions in a way that it
adverse to such directors, executive officers and employees.
 
  The Registrant's policy is to enter into indemnification agreements with
each of its directors and executive officers that provide the maximum
indemnity allowed to directors and executive officers by Section 145 of the
Delaware General Corporation Law and the Amended and Restated Bylaws, as well
as certain additional procedural protections. In addition, the indemnity
agreement provide that directors and executive officers will be indemnified to
the fullest possible extent not prohibited by law against all expenses
(including attorney's fees) and settlement amounts paid or incurred by them in
any action or proceeding, including any derivative action by or in the right
of the Registrant, on account of their services as directors or executive
officers of the Registrant or as directors or officers of any other company or
enterprise when they are serving in such capacities at the request of the
Registrant. The Company will not be obligated pursuant to the indemnity
agreements to indemnify or advance expenses to an indemnified party with
respect to proceedings or claims initiated by the indemnified
 
                                     II-1

 
party and not by way of defense, except with respect to proceedings
specifically authorized by the Board of Directors or brought to enforce a
right to indemnification under the indemnity agreement, the Company's Amended
and Restated Bylaws or any statute or law. Under the agreements, the Company
is not obligated to indemnify the indemnified party (i) for any expenses
incurred by the indemnified party with respect to any proceeding instituted by
the indemnified party to enforce or interpret the agreement, if a court of
competent jurisdiction determines that each of the material assertions made by
the indemnified party in such proceeding was not made in good faith or was
frivolous; (ii) for any amounts paid in settlement of a proceeding unless the
Company consents to such settlement; (iii) with respect to any proceeding
brought by the Company against the indemnified party for willful misconduct,
unless a court determines that each of such claims was not made in good faith
or was frivolous; (iv) on account of any suit in which judgment is rendered
against the indemnified party for an accounting of profits made from the
purchase or sale by the indemnified party of securities of the Company
pursuant to the provisions of (S) 16(b) of the Securities Exchange Act of 1934
and related laws; (v) on account of the indemnified party's conduct which is
finally adjudged to have been knowingly fraudulent or deliberately dishonest,
or to constitute willful misconduct or a knowing violation of the law; (vi) an
account of any conduct from which the indemnified party derived an improper
personal benefit; (vii) on account of conduct the indemnified party believed
to be contrary to the best interests of the Company or its stockholders;
(viii) on account of conduct that constituted a breach of the indemnified
party's duty of loyalty to the Company or its stockholders; or (ix) if a final
decision by a court having jurisdiction in the matter shall determine that
such indemnification is not lawful.
 
  The indemnification provision in the Amended and Restated Bylaws and the
indemnification agreements entered into between the Registrant and its
directors and executive officers, may be sufficiently broad to permit
indemnification of the Registrant's officers and directors for liabilities
arising under the 1933 Act.
 
  Reference is made to the following documents filed as exhibits to this
Registration Statement regarding relevant indemnification provisions described
above and elsewhere herein:
 


                                                                       EXHIBIT
   DOCUMENT                                                            NUMBER
   --------                                                            -------
                                                                    
   Form of Underwriting Agreement.....................................   1.1
   Restated Certificate of Incorporation..............................   3.2
   Amended and Restated Bylaws........................................   3.4
   Form of Indemnification Agreement entered into by the Registrant
    with each of its directors and executive officers.................  10.1

 
ITEM 15. RECENT SALES OF UNREGISTERED SECURITIES
 
  Since March 31, 1993, the Registrant has issued and sold the following
securities (assuming the Company's one-for-three stock split):
 
    1. From March 31, 1993 to March 31, 1996 the Registrant issued and sold
  118,427 shares of Common Stock to directors, employees and consultants at
  prices ranging from $0.30 to $3.00 per share, upon exercise of stock
  options pursuant to the Registrant's 1987 Incentive Stock Plan.
 
    2. On April 21, 1993, the Registrant issued and sold 507,541 shares of
  Series C Preferred Stock to a total of 5 investors at $7.50 per share.
 
    3. From November 21, 1994 to February 8, 1996 the Registrant issued
  warrants to purchase an aggregate of 34,471 shares of Series D Preferred
  Stock to a total of 5 investors with an exercise price of $7.50 per share.
 
    4. On November 21, 1994, the Registrant issued and sold 1,614,284 shares
  of Series D Preferred Stock to a total of 19 investors at $7.50 per share.
 
    5. On April 11, 1995, the Registrant issued 9,968 shares of Common Stock
  to a total of 10 employees as bonuses at a fair market value of $1.50 per
  share.
 
                                     II-2

 
    6. On February 6, 1996, the Registrant issued and sold 284,594 shares of
  Series D Preferred Stock to a total of 18 investors at $7.50 per share.
 
    7. On April 22, 1996, the Registrant issued and sold 4,167 shares of
  Common Stock to a director of the Company at $12.00 per share.
 
  The sale of the above securities were deemed to be exempt from registration
under the Securities Act in reliance on Section 4(2) of the Securities Act or
Regulation D promulgated thereunder, or rule 701 promulgated under Section
3(b) of the Securities Act as transactions by an issuer not involving any
public offering or transactions pursuant to compensatory benefit plans and
contracts relating to compensation as provided under such Rule 701. The
recipients of securities in each such transaction represented their intentions
to acquire the securities for investment only and not with a view to or for
sale in connection with any distribution thereof and appropriate legends were
affixed to the share certificates issued in such transactions. All recipients
had adequate access, through their relationship with the Registrant, to
information about the Registrant.
 
ITEM 16. EXHIBITS AND FINANCIAL STATEMENT SCHEDULES
 
  (a) Exhibits
 
   
    
   1.1 Form of Underwriting Agreement.
  *3.1 Certificate of Incorporation of the Registrant.
  *3.2 Form of Restated Certificate of Incorporation of the Registrant to be
       filed prior to the effective date of the offering made under this
       Registration Statement.
  *3.3 Form of Restated Certificate of Incorporation to be filed immediately
       following the closing of the offering made under this Registration
       Statement.
  *3.4 Amended and Restated Bylaws of the Registrant.
  *4.1 Specimen Common Stock Certificate.
  *4.2 Amended and Restated Investor Rights Agreement.
  *5.1 Opinion of Wilson Sonsini Goodrich & Rosati Professional Corporation.
 *10.1 Form of Indemnification Agreement between the Registrant and each of its
       directors and executive officers.
 *10.2 1987 Incentive Stock Plan, as amended and related agreements.
 *10.3 1996 Stock Plan and form of Stock Option Agreement thereunder.
 *10.4 Employee Stock Purchase Plan and forms of agreement thereunder.
       1996 Director Option Plan and form of Director Stock Option Agreement
 *10.5 thereunder.
       Asset Purchase Agreement between the Registrant and Purus, Inc. dated
 *10.6 January 4, 1996.
       Lease dated June 12, 1995 between the Registrant and Westmark Metro
 *10.7 Plaza, Inc., as amended.
       Lease dated June 24, 1995 between the Registrant and American General
 *10.8 Life Insurance Company.
 *10.9 Loan and Security Agreement between the Registrant and Cupertino
       National Bank and Trust, dated December 15, 1995.
  11.1 Statement of computation of pro forma Common Shares and Equivalents.
 *21.1 Subsidiary of the Registrant.
 *23.1 Consent of Counsel (included in Exhibit 5.1).
 *23.2 Consent of Woodcock Washburn Kurtz Mackiewicz & Norris.
 *23.3 Consent of Arthur Andersen LLP (see page II-7).
 *24.1 Power of Attorney (see page II-5).
 *27.1 Financial Data Schedule.
    
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* previously filed
 
  (b) Financial Statement Schedules
 
      Report of Independent Public Accountants on Schedule
 
      II--Valuation and Qualifying Accounts
 
  Schedules not listed above have been omitted because the information
required to be set forth therein is not applicable or is shown in the
financial statements or notes thereto.
 
                                     II-3

 
ITEM 17. UNDERTAKINGS
 
  The Registrant hereby undertakes to provide to the Underwriters at the
closing specified in the Underwriting Agreement, certificates in such
denominations and registered in such names as required by the Underwriters to
permit prompt delivery to each purchaser.
 
  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 Delaware General Corporation Law, the Restated
Certificate of Incorporation or Bylaws of the Registrant, the Underwriting
Agreement or otherwise, the Registrant has been advised that in the opinion of
the Securities and Exchange Commission such indemnification is against public
policy as expressed in the 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 director, officer or
controlling person in connection with the securities being registered
hereunder, 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.
 
  The undersigned Registrant hereby undertakes that:
 
    (1) For purposes of determining any liability under the Act, the
  information omitted from the form of Prospectus filed as part of this
  Registration Statement in reliance upon Rule 430A and contained in a form
  of Prospectus filed by the Registrant pursuant to Rule 424(b)(1) or (4) or
  497(h) under the Act shall be deemed to be part of this Registration
  Statement as of the time it was declared effective.
 
    (2) For the purpose of determining any liability under the Act, each
  post-effective amendment that contains a form of Prospectus shall be deemed
  to be a new Registration Statement relating to the securities offered
  therein, and the offering of such securities at that time shall be deemed
  to be the initial bona fide offering thereof.
 
                                     II-4

 
                                  SIGNATURES
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THE REGISTRANT
HAS DULY CAUSED THIS POST-EFFECTIVE AMENDMENT NO. 1 TO REGISTRATION STATEMENT
ON FORM S-1 TO BE SIGNED ON ITS BEHALF BY THE UNDERSIGNED, THEREUNTO DULY
AUTHORIZED, IN THE CITY OF SAN JOSE, STATE OF CALIFORNIA, ON THIS 19TH DAY OF
JUNE, 1996.     
 
                                          Thermatrix Inc.
                                                  
                                               /s/ Steven J. Guerrettaz     
                                          By: _________________________________
                                                
                                                 STEVEN J. GUERRETTAZVICE
                                             PRESIDENT, FINANCE AND ACCOUNTING
                                             AND CHIEF FINANCIAL OFFICER     
   
  PURSUANT TO THE REQUIREMENTS OF THE SECURITIES ACT OF 1933, THIS POST-
EFFECTIVE AMENDMENT NO. 1 TO REGISTRATION STATEMENT HAS BEEN SIGNED BY THE
FOLLOWING PERSONS IN THE CAPACITIES AND ON THE DATES INDICATED.     
 
    
 

             SIGNATURES                        TITLE                         DATE
             ----------                        -----                         ---- 
                                                                    
     */s/ John T. Schofield               Chairman of the Board,         June 19, 1996
- -------------------------------------       President and Chief
          JOHN T. SCHOFIELD                 Executive Officer
                                            (Principal Executive 
                                            Officer) 
                                          
    /s/ Steven J. Guerrettaz              Vice President, Finance and    June 19, 1996
- -------------------------------------       Accounting and Chief             
        STEVEN J. GUERRETTAZ                Financial Officer
                                            (Principal Financial and
                                            Accounting Officer)  
                                            
        */s/ Robi Blumenstein                Director                    June 19, 1996 
- -------------------------------------                           
          ROBI BLUMENSTEIN                                           
 
      */s/ Harry J. Healer, Jr.              Director                    June 19, 1996
- -------------------------------------                           
        HARRY J. HEALER, JR.                                         
 
                                             Director
- -------------------------------------
           REBECCA P. MARK
 
     
                                     II-5

 
     
 
 
             SIGNATURES                      TITLE                   DATE
             ----------                      -----                   ---- 
                                                            
         */s/ Robert W. Page               Director              June 19, 1996
- -------------------------------------                                        
           ROBERT W. PAGE                                      
 
                                           Director
- -------------------------------------
            FRANK R. POPE
 
         */s/ John M. Toups                Director              June 19, 1996
- -------------------------------------                                        
            JOHN M. TOUPS                                      
    
    /s/ Steven J. Guerrettaz 
*By _________________________________
  STEVEN J. GUERRETTAZ ATTORNEY-IN-
                FACT 
     

                                      II-6

 
                                 EXHIBIT INDEX
 
   

                                                                  SEQUENTIALLY
 EXHIBIT                   EXHIBIT DESCRIPTION                    NUMBERED PAGE
 -------                   -------------------                    -------------
                                                            
   1.1   Form of Underwriting Agreement.
  *3.1   Certificate of Incorporation of the Registrant.
  *3.2   Form of Restated Certificate of Incorporation of the
         Registrant to be filed prior to the effective date of
         the offering made under this Registration Statement.
  *3.3   Form of Restated Certificate of Incorporation to be
         filed immediately following the closing of the
         offering made under this Registration Statement.
  *3.4   Amended and Restated Bylaws of the Registrant.
  *4.1   Specimen Common Stock Certificate.
  *4.2   Amended and Restated Investor Rights Agreement.
         Opinion of Wilson Sonsini Goodrich & Rosati
  *5.1   Professional Corporation.
 *10.1   Form of Indemnification Agreement between the
         Registrant and each of its directors and executive
         officers.
         1987 Incentive Stock Plan, as amended and related
 *10.2   agreements.
         1996 Stock Plan and form of Stock Option Agreement
 *10.3   thereunder.
         Employee Stock Purchase Plan and forms of agreement
 *10.4   thereunder.
         1996 Director Option Plan and form of Director Stock
 *10.5   Option Agreement thereunder.
 *10.6   Asset Purchase Agreement between the Registrant and
         Purus, Inc. dated January 4, 1996.
 *10.7   Lease dated June 12, 1995 between the Registrant and
         Westmark Metro Plaza, Inc., as amended.
 *10.8   Lease dated June 24, 1995 between the Registrant and
         American General Life Insurance Company.
 *10.9   Loan and Security Agreement between the Registrant and
         Cupertino National Bank and Trust, dated December 15,
         1995.
         Statement of computation of pro forma Common Shares
  11.1   and Equivalents.
 *21.1   Subsidiary of the Registrant.
 *23.1   Consent of Counsel (included in Exhibit 5.1).
         Consent of Woodcock Washburn Kurtz Mackiewicz &
 *23.2   Norris.
 *23.3   Consent of Arthur Andersen LLP (see page II-7).
 *24.1   Power of Attorney (see page II-5).
 *27.1   Financial Data Schedule.
    
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* previously filed