SEMICONDUCTOR DEVICE AND MANUFACTURE THEREOF

PURPOSE:To allow excessive carriers to be discharged and to improve breakdown voltages by providing in a substrate a region where conductivity is high, and reducing generation of excessive carriers within the substrate and a resistance against an accumulation region. CONSTITUTION:An N-channel MIS transistor comprising a source 1, a drain 2, and a gate 3 is arranged on a P-type silicon substrate, wherein a P-layer 16 which is heavily doped compared to a substrate introduced through a groove- shaped vertical hole is formed, the groove having a highly conductive electrode material 17 buried therein which is in contact with the P-layer 16. According to the constitution, the distance between the accumulation region 8, and the buried region 17 which will be a substrate contact can be short and a resistance therebetween can drastically be reduced by the heavy doping of the P-layer, whereby a source-drain breakdown voltage against avalanche breakdown can be improved.