Patent ID: 8148783

Claim:
A semiconductor device comprising: a semiconductor layer made of a first conductivity type semiconductor material; a first conductivity type first impurity region, formed on a surface layer portion of the semiconductor layer, having an impurity concentration higher than the impurity concentration in the semiconductor layer; a second conductivity type body region formed on the surface layer portion of the semiconductor layer at an interval from the first impurity region; a first conductivity type second impurity region, formed on a surface layer portion of the body region, having an impurity concentration higher than the impurity concentration in the semiconductor layer; a field insulating film formed on a portion of the surface of the semiconductor layer between the first impurity region and the second impurity region at an interval from the second impurity region; a gate insulating film formed on the surface of the semiconductor layer between the second impurity region and the field insulating film; a gate electrode formed on the gate insulating film; a first floating plate provided in the form of a ring having a constant width on the field insulating film; and a second floating plate provided in the form of a ring having a constant width on the same layer above the first floating plate, wherein the first floating plate and the second floating plate are formed by not less than three in total so that the peripheral lengths at the centers in the width direction thereof are entirely different from one another, alternately arranged in plan view so that the one having a relatively smaller peripheral length is stored in an inner region of the one having a relatively larger peripheral length, and formed to satisfy the relational expression: L/d=constant (L: the outer periphery of the inner one of the first and second floating plates adjacent to each other in plan view, d: the distance between the outer periphery of the plate defining L and the inner periphery of the first or second floating plate adjacent to the plate to be opposed to the outer periphery thereof).