Semiconductor device

A semiconductor device, comprising:

• a semiconductor layer having a first surface and a second surface opposite to the first surface, the semiconductor layer including:
• a gradient impurity concentration region of a first conductivity type;
• a first semiconductor region of a second conductivity type located between the gradient impurity concentration region and the first surface;
• a second semiconductor region of the first conductivity type located between the first semiconductor region and the first surface;
• one or more first trenches extending from the first surface into the gradient impurity concentration region;
• and
• a second trench extending from the first surface into the gradient impurity concentration region and surrounding the first trench;
• a first electrode provided in the first trench and surrounded by a first insulating film in the first trench;
• a second electrode provided in the first trench and surrounded by a second insulating film in the first trench;
• a third electrode provided in the second trench and surrounded by a third insulating film in the second trench, wherein
• the gradient impurity concentration region continuously includes a first subregion at a first depth range from the first surface, a second subregion at a second depth range from the first surface that is shallower than the first depth range, and a third subregion at a third depth range from the first surface that is shallower than the second depth range, and
• the first subregion has a first impurity concentration, the second subregion has a second impurity concentration, and the third subregion has a third impurity concentration lower than the second impurity concentration.