Patent ID: 8314458

Claim:
A semiconductor transistor device comprising: a semiconductor layer of a first general conductivity type; a drain diffusion layer of the first general conductivity type formed in the semiconductor layer, the drain diffusion layer comprising a drain contact region configured to receive a drain potential from a device external to the transistor device or supply a drain potential to a device external to the transistor device; a backgate diffusion layer of a second general conductivity type formed in the semiconductor layer; a source diffusion layer of the first general conductivity type formed in the backgate diffusion layer; and an additional diffusion layer of the second general conductivity type formed in the drain diffusion layer so that at least part of the additional diffusion layer is disposed between the backgate diffusion layer and the drain contact region, wherein a sidewall of the additional diffusion layer and a sidewall of the drain contact region are in direct contact so as to form a PN junction, and the PN junction is configured to break down upon receiving a surge voltage at the drain contact region.