Patent ID: 8723258

Claim:
A semiconductor transistor comprising: a semiconductor layer of a first general conductivity type; a drift layer of the first general conductivity type formed in a surface portion of the semiconductor layer; a drain layer of the first general conductivity type formed in a surface portion of the drift layer; a base layer of a second general conductivity type formed in a surface portion of the semiconductor layer apart from the drift layer; a source layer of the first general conductivity type formed in a surface portion of the base layer and comprising a plurality of openings; a contact layer of the second general conductivity type filling each of the openings in the source layer so that there is a distance between an edge of the contact layer and a corresponding edge of the source layer; a gate insulation film covering at least part of the base layer and part of the semiconductor layer; a gate electrode disposed on the gate insulation film; and another semiconductor layer of the second general conductivity type contiguous to the contact layer and extending from the edge of the contact layer into the base layer under the source layer around the opening, wherein an extended portion of the another semiconductor layer is connected with another extended portion of the another semiconductor layer extending from an edge of another contact layer.