In producing a top gate type or a bottom gate type thin film transistor (TFT), after a metal film for forming silicide is formed on a semiconductor active layer provided on an insulating surface, an N-type or P-type impurity ion is introduced into the semiconductor active layer using an anodizable gate electrode and an anodic oxide formed on the surface of the gate electrode as masks. The exposing portion of the semiconductor active layer is reacted with the metal film, so that a silicide layer is formed in the portion. Then, non-reacted portion of the metal film is removed.