A manufacturing method of a semiconductor device includes a step of preparing a semiconductor substrate having a first main surface and a second main surface, a step of forming a recess in the first main surface and embedding an insulating film in the recess, a step of forming a polysilicon film on the insulating film, a step of forming an interlayer insulating film on the first main surface so as to cover the insulating film and the polysilicon film, and a step of forming a first contact hole and a second contact hole. The semiconductor substrate has a first impurity diffusion region formed in the first main surface, and a second impurity diffusion region in contact with a portion of the first impurity diffusion region, the portion being closer to the second main surface.