Method of manufacturing MIS semiconductor device that can control gate depletion and has low resistance gate electrode to which germanium is added

According to a method of manufacturing a MIS semiconductor device of the present invention, a gate insulating film is formed on a silicon substrate, and a silicon thin film is deposited on the gate insulating film, whereafter a silicon film containing germanium is deposited on the silicon thin film and an amorphous silicon film is deposited on the germanium-containing silicon film. Further, heat treatment is performed to diffuse the germanium in the germanium-containing silicon film into the silicon thin film, and a metal film is deposited on the amorphous silicon film and heat treatment is performed to cause a silicidation reaction to occur with the metal film to form a silicide film. Therefore, the germanium-containing silicon film which can control gate depletion can be formed stably with a good reproducibility. Further, since the silicide film on the gate electrode is formed on the silicon film, it can be formed with a low resistance.