A semiconductor storage device according to the present embodiment includes a semiconductor substrate. A tunnel insulating film is provided on the semiconductor substrate. A charge accumulation layer is provided on the tunnel insulating film. An intermediate dielectric film is provided on the charge accumulation layer. A control gate electrode is formed on the intermediate dielectric film. The intermediate dielectric film includes a laminated film of silicon oxide films of multiple layers and silicon nitride films of at least one layer, and a silicon oxynitride film provided between adjacent ones of the silicon oxide films and the silicon nitride films.