Patent ID: 7399999

Claim:
A semiconductor device comprising: a semiconductor layer comprising an actual operation region in which a plurality of cells are formed and a guard ring region disposed around the actual operation region, the cells comprising corresponding source, gate and drain regions; a diffusion region which forms a boundary between the actual operation region and the guard ring region and is formed in a surface of the semiconductor layer; a thermally-grown oxide film formed on the surface of the semiconductor layer; a CVD oxide film formed on the thermally-grown oxide film; a metal wiring layer electrically connected to the diffusion region and formed on the CVD oxide film, the metal wiring layer being connected to the diffusion region through a contact region provided in the first thermally-grown oxide film and the CVD oxide film; and a gate electrode disposed on the gate regions and electrically connected to the metal wiring layer, wherein the thermally-grown oxide film comprises first and second thermally-grown oxide films juxtaposed on the semiconductor layer, the second thermally-grown oxide film is thicker than the first thermally-grown oxide film and is formed on the guard ring region, and the first thermally-grown oxide film is formed on at least part of the actual operation region, and one end of the metal wiring layer extends toward the side of the guard ring region beyond one end of the diffusion region, said one end being the farther end of said metal wiring layer from the actual operation region.