To provide a method for manufacturing a semiconductor storage device capable of reducing a margin fault due to shorting of metal wiring and the high resistance of a gate electrode by preventing a metal electrode from being oxidized in a heat treating step at the time of forming a sidewall of a gate electrode.

The method for manufacturing the semiconductor storage device comprises the steps of forming a nitride film 113 on an upper layer of a metal electrode layer 111 on a gate electrode layer, and removing a gate oxide film 106 under etching conditions in which an etching rate of the nitride film 113 is slower than that of the film 106 in a source region forming step. Thus, since the nitride film 113 is retained on the metal electrode layer even when the film 106 is removed in the source region forming step, the metal electrode layer 111 can be prevented from being oxidized in the later heat treating step.