EXHIBIT 21

                               SEMCO ENERGY, INC.

                              List of Subsidiaries
                         Exhibit 21 to Form 10-K (2004)

As of December 31, 2004, 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

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

- -     SEMCO Georgia Construction Company (formerly known as Flint Construction
      Company), a Georgia corporation (a subsidiary of SEMCO Construction Parent
      Company)

- -     SEMCO Iowa Construction Company (formerly known as Iowa Pipeline
      Associates, Inc.), a Michigan corporation (a subsidiary of SEMCO
      Construction Parent Company)

- -     Long's Underground Technologies, Inc., a Michigan corporation (a
      subsidiary of SEMCO Construction Parent Company)

- -     SEMCO Michigan Construction Company (formerly known as Sub-Surface
      Construction Co.), a Michigan corporation (a subsidiary of SEMCO
      Construction Parent Company)

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

- -     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.)

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 Battle Creek Gas Company and SEMCO Energy
      Gas Company.

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

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