Semiconductor device

A semiconductor device comprising:

• a silicon substrate that includes a high-concentration layer containing first conductivity type impurities;
• a low-concentration layer formed on the high-concentration layer and containing first conductivity type impurities at a concentration lower than a concentration of the high-concentration layer;
• a first electrode and a second electrode formed on the low-concentration layer;
• a vertical semiconductor element that allows current to flow between the second electrode and the high-concentration layer;
• and
• a first trench unit that realizes electric connection between the first electrode and the high-concentration layer,
• wherein the first trench unit consists of first polysilicon containing first conductivity type impurities, and a diffusion layer configured to surround the first polysilicon in a plan view and to contain first conductivity type impurities,
• the first polysilicon is configured to reach the high-concentration layer from an upper surface of the low-concentration layer by penetrating the low-concentration layer, and
• respective concentrations of the first conductivity type impurities contained in the first polysilicon and in the diffusion layer are kept constant in a direction from the low-concentration layer to the high-concentration layer.