Mis semiconductor device with low on resistance and high breakdown voltage

Abstract

The invention provides a semiconductor device, manufactured with low manufacturing costs, that prevents the breakdown voltage from lowering. The semiconductor device according to the invention includes a p-type highly resistive semiconductor substrate; an n-type offset region in the surface portion of the substrate; a p-type base region in the surface portion of the substrate, the base region including an n -type source region in the surface portion thereof, the base region including a channel portion in the extended portion thereof extended between the source region and the n-type offset region; a p-type offset region in the surface portion of the n-type offset region, the potential of the p-type offset region being fixed at the source potential; an n -type drain region in the surface portion of the n-type offset region; a field oxide film on the p-type offset region; a gate oxide film on the channel portion of the base region; a gate electrode on the gate oxide film; a source electrode on source region; a drain electrode on the drain region; an interlayer film; a protection film; and a spiral polysilicon thin film on the field oxide film, one end of the thin film being connected to the drain electrode, another end of the thin film being connected to the source electrode, the thin film being formed of pn-diodes connected in series.