This semiconductor device comprises the following: a silicon substrate that has a high-concentration layer containing a first-conductivity-type impurity; a low-concentration layer that is formed on top of the high-concentration layer and contains a first-conductivity-type impurity; a first electrode and a second electrode both formed on top of the low-concentration layer; a vertical semiconductor element that causes current to flow between the second electrode and the high-concentration layer; and a first trench section that electrically connects the first electrode and the high-concentration layer to each other. The first trench section comprises the following: first polysilicon containing a first-conductivity-type impurity; and a diffusion layer that contains a first-conductivity-type impurity and, in a planar view, surrounds the first polysilicon. The first polysilicon is formed so as to penetrate the low-concentration layer and reach the high-concentration layer, and the concentration of the first-conductivity-type impurity in the first polysilicon and the diffusion layer is constant in the direction from the low-concentration layer to the high-concentration layer.