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 .