Semiconductor device

A semiconductor device comprising:

• a semiconductor substrate having a drift layer with a first conductive type;
• a base layer having a second conductive type and disposed on the drift layer;
• a carrier storage layer having the first conductive type with an impurity concentration higher than the drift layer, and arranged over the drift layer;
• a collector layer having the second conductive type and arranged on the drift layer opposite to the base layer;
• a plurality of trenches penetrating the base layer and the carrier storage layer, reaching the drift layer, and arranged along one direction of a planar direction of the semiconductor substrate;
• a gate insulation film arranged on a sidewall of each trench;
• a gate electrode arranged on the gate insulation film;
• and
• an emitter region having the first conductive type, arranged in a surface portion of the base layer, and contacting each trench, wherein:
• a thickness of at least a portion of a part of the gate insulation film arranged on a sidewall of each trench disposed on a collector layer side from a peak position, at which the impurity concentration of the carrier storage layer is highest, is thicker than a thickness of another part of the gate insulation film arranged on the sidewall of each trench disposed on an opening portion side of the trench from the peak position.