Trenched high breakdown voltage semiconductor device

A high breakdown voltage semiconductor device comprising:

• an SOI semiconductor substrate having first and second main surfaces opposite to each other, said SOI semiconductor substrate having a substrate arranged nearer said second main surface and a semiconductor layer arranged nearer said first main surface and insulated from said substrate, and also having a plurality of trenches provided at said first main surface;
• a first impurity region of a first conductivity type formed within a region of said semiconductor layer sandwiched between one and another trenches of said plurality of trenches at a sidewall surface of said one trench;
• a second impurity region of a second conductivity type formed within said region sandwiched between said one and another trenches at a sidewall surface of said another trench, and forming a pn junction together with said first impurity region;
• a third impurity region of the second conductivity type formed within said semiconductor layer;
• a fourth impurity region of the first conductivity type formed on at least one of said first main surface and a sidewall surface of said one trench such that said fourth impurity region is disposed opposite to said first impurity region with said third impurity region disposed therebetween;
• and
• a gate electrode layer opposite to said third impurity region, sandwiched between said first and fourth impurity regions, with a gate insulating layer disposed therebetween;
• wherein
• said first impurity region has a distribution of concentration of an impurity diffused from a sidewall surface of said one trench;
• and
• said second impurity region has a distribution of concentration of an impurity diffused from a sidewall surface of said another trench;
• a source electrode formed on said first main surface electrically connected with said third and fourth impurity regions and
• a drain electrode formed on said first main surface electrically connected with said first impurity region.