Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a semiconductor substrate having a first main surface and a second main surface, the semiconductor substrate having an n-type drift layer provided therein;
• a p-type layer provided between the first main surface of the semiconductor substrate and the drift layer;
• and
• an n-type high-concentration layer provided between the second main surface of the semiconductor substrate and the drift layer, the n-type high-concentration layer including a plurality of buffer layers, wherein
• a carrier concentration of the semiconductor device is higher in the n-type high-concentration layer than in the semiconductor substrate, and
• in one of the plurality of buffer layers, the carrier concentration decreases both upward and downward in a depth direction of the semiconductor device, from a peak concentration thereof at a peak position to a pre-determined concentration at a first depth position and a second depth position respectively above and below the peak position, the first depth position and the second depth position having the same pre-determined concentration that is a half of the peak concentration, a first width being a distance in the depth direction between the first depth position and the peak position, a second width being a distance in the depth direction between the peak position and the second depth position, the first width being larger than the second width.