Patent ID: 7279768

Claim:
A semiconductor device comprising: a semiconductor substrate of one conductivity type; an epitaxial layer of an opposite conductivity type formed on the semiconductor substrate; a buried diffusion layer of an opposite conductivity type formed across the semiconductor substrate and the epitaxial layer; a buried diffusion layer of one conductivity type, which is formed on the buried diffusion layer of the opposite conductivity type and which has a first junction region with the buried diffusion layer of the opposite conductivity type; a first diffusion layer of one conductivity type, which is formed in the epitaxial layer and which is used as a back gate region; a first diffusion layer of an opposite conductivity type, which is formed in the first diffusion layer of the one conductivity type and which is used as a source region: a gate oxide film and a gate electrode formed on the epitaxial layer; a second diffusion layer of an opposite conductivity type, which is formed in the epitaxial layer, which is used as a drain region, and which has a second junction region with the first diffusion layer of the one conductivity type; and a third diffusion layer of an opposite conductivity type, which is formed in the epitaxial layer and which is electrically connected to the second diffusion layer of the opposite conductivity type above the epitaxial layer, wherein a breakdown voltage of the first junction region is lower than that of the second junction region.