Patent ID: 8013416

Claim:
A semiconductor device comprising: a semiconductor substrate; a first region defined on the semiconductor substrate and having a first device formation region isolated by a device isolation portion having an STI structure formed by filling an insulator in a trench formed in the semiconductor substrate, wherein a surface of the insulator of the STI structure and a surface of the semiconductor substrate are both arranged in a common plane; a first device provided in the first device formation region; a second region defined on the semiconductor substrate conterminously to the first region and having a second device formation region defined in a well; and a second device provided in the second device formation region and having a higher breakdown voltage than the first device, the second device having a drift drain structure in which a LOCOS oxide film thicker than a gate insulation film thereof is disposed at an edge of a gate electrode thereof, wherein the device isolation portion includes, at a boundary between the first region and the second region, the STI structure in contact with the first region and the LOCOS oxide film in contact with the second region, the insulator of the STI structure and the LOCOS oxide film are continuous at the boundary between the first region and the second region, and the STI structure at the boundary has a trench that extends from the first region to an end portion of the well with a uniform depth.