Patent ID: 7291883

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 formed on the buried diffusion layer of the opposite conductivity type and having a first junction region with the buried diffusion layer of the opposite conductivity type; a first diffusion layer of one conductivity type formed in the epitaxial layer and used as a drain region; a first diffusion layer of an opposite conductivity type formed in the first diffusion layer of the one conductivity type and used as a back gate region as well as having a second junction region with the first diffusion layer of the one conductivity type; a second diffusion layer of one conductivity type formed in the first diffusion layer of the opposite conductivity type and used as a source region; a gate oxide film and a gate electrode formed on the epitaxial layer; and a second diffusion layer of an opposite conductivity type formed in the epitaxial layer and electrically connected to the second diffusion layer of the one conductivity type above the epitaxial layer, wherein a breakdown voltage of the first junction region is lower than a breakdown voltage of the second junction region.