EXHIBIT 21

                               SEMCO ENERGY, INC.

                              List of Subsidiaries
                         Exhibit 21 to Form 10-K (2003)

As of December 31, 2003, the subsidiaries of SEMCO Energy, Inc. (the Registrant)
were:


- -    Alaska Pipeline Company, an Alaska corporation

- -    NORSTAR Pipeline Company, Inc., an Alaska corporation (a subsidiary of
     Alaska Pipeline Company)

- -    Aretech Information Services, Inc., a Michigan corporation

- -    Hotflame Gas, Inc., a Michigan corporation

- -    EnStructure Corporation (formerly known as Sub-Surface Resources, Inc. and
     prior thereto, NATCOMM, Inc.), a Michigan corporation

- -    Flint Construction Company, a Georgia corporation (a subsidiary of
     EnStructure Corporation)

- -    Iowa Pipeline Associates, Inc., a Michigan corporation (a subsidiary of
     EnStructure Corporation)

- -    K & B Construction, Inc., a Kansas corporation (a subsidiary of Iowa
     Pipeline Associates, Inc.)

- -    Long's Underground Technologies, Inc., a Michigan corporation (a subsidiary
     of EnStructure Corporation)

- -    Sub-Surface Construction Co., a Michigan corporation (a subsidiary of
     EnStructure Corporation)

- -    SEMCO Energy Ventures, Inc., a Michigan corporation

- -    SEMCO Arkansas Pipeline Company, a Michigan corporation (a subsidiary of
     SEMCO Energy Ventures, Inc.)

- -    SEMCO Gas Storage Company, a Michigan corporation (a subsidiary of SEMCO
     Energy Ventures, Inc.)

- -    SEMCO Pipeline Company, a Michigan corporation (a subsidiary of SEMCO
     Energy Ventures, Inc.)

- -    Southeastern Development Company, a Michigan corporation (a subsidiary of
     SEMCO Energy Ventures, Inc.)

- -    Southeastern Financial Services, Inc., a Michigan corporation (a subsidiary
     of SEMCO Energy Ventures, Inc.)


Each of the above-listed companies does business only under its respective
corporate name as indicated above, except as follows:

- -    SEMCO Energy, Inc. does business in Alaska under the name ENSTAR Natural
     Gas Company and in Michigan as SEMCO Energy Gas Company.

- -    Aretech Information Services, Inc. does business in Michigan under the name
     Arenet.net and Arenet.

- -    Flint Construction Company does business in Oklahoma and West Virginia
     under the name FCCO, Inc.

- -    Sub-Surface Construction Co. does business in Ohio under the name Sub
     Surface Gas Services and Main Construction Co.