Successful synthesis of room-temperature ferromagnetic semiconductors, Cu-codoped ZnCoO films are obtained by sol-gel method. It is found that the essential ingredient in achieving room-temperature ferromagnetism is Cu-codoping. By Hall-effect measurement a p-type conductivity was observed for the Cu-codoped films, the hole concentration increases with the increase in Cu concentration. XPS result confirmed Cu ions are univalent in the films, which induced the room-temperature ferromagnetism. (C) 2008 Elsevier B.V. All rights reserved.