An n− type semiconductor region is provided with an n− diffusion region serving as a drain region, and at one side of the n− diffusion region a p diffusion region and an n+ diffusion region serving as a source region are provided. At an other side of the n− diffusion region a trench is provided and has an insulator introduced therein. Immediately under the n− diffusion region a p− buried layer is provided. In a region of the n− semiconductor region an n+ diffusion region to which a high potential is applied is provided and electrically connected to the n− diffusion region by an interconnect having a resistor. On a surface of a portion of the p diffusion region that is sandwiched between the n+ diffusion region and the n− diffusion region a gate electrode is provided, with a gate insulation film posed therebetween.