Semiconductor device

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.