The present invention provides a semiconductor device which includes a gate electrode shaped in the form of an approximately quadrangular prism, including a laminated body of a gate oxide layer, a gate polysilicon layer and a gate silicon nitride layer provided in a first conduction type substrate, a second conduction type implantation region provided in a region outside the gate electrode, a sidewall that exposes a top face of the gate electrode and is formed by laminating a sidewall mask oxide layer covering side surfaces, an electron storage nitride layer and a sidewall silicon oxide layer, and a source/drain diffusion layer provided in the first conduction type substrate exposed from the gate electrode and the sidewall.