Lateral semiconductor device and vertical semiconductor device

A lateral semiconductor device comprising:

• a first conductivity type base layer having resistance higher than that of a first conductivity type buffer layer;
• said first conductivity type buffer layer selectively formed in the surface portion of said first conductivity type base layer;
• a second conductivity type drain layer selectively formed in the surface portion of said first conductivity type buffer layer;
• a second conductivity type base layer selectively formed in the surface portion of said first conductivity type base layer so as to surround said first conductivity type buffer layer with a spacing therebetween;
• a first conductivity type source layer selectively formed in the surface portion of said second conductivity type base layer;
• a gate electrode formed via a gate insulating film on the surface of said second conductivity type base layer sandwiched between said first conductivity type base layer and said first conductivity type source layer;
• a source electrode in contact with said second conductivity type base layer and said first conductivity type source layer;
• and
• a drain electrode in contact with said second conductivity type drain layer,
• wherein said second conductivity type drain layer has a structure in which said first conductivity type buffer layer not in contact with said drain electrode is exposed in a portion of said second conductivity type drain layer.