Semiconductor device and method of manufacturing the same

A semiconductor device, comprising:

• a semiconductor substrate;
• a drain region of a first conductivity type formed on the semiconductor substrate;
• a source region of the first conductivity type formed on the semiconductor substrate;
• a body region of a second conductivity type formed between the drain region and the source region;
• a gate insulating film formed on the body region;
• a gate electrode formed on the gate insulating film;
• a trench formed in the drain region;
• and
• a thick insulating film formed in the trench, and having a thickness larger than a thickness of the gate insulating film,
• the trench having a first trench side surface opposed to the body region, a second trench side surface which is opposed to the first trench side surface and the body region and is formed farther away from the body region than the first trench side surface, a trench bottom surface, and a first corner portion formed at an intersecting portion between the trench bottom surface and the first trench side surface as seen in cross-sectional view and a second corner portion formed at an intersecting portion between the trench bottom surface and the second trench side surface as seen in cross-sectional view,
• the drain region comprising:
• a first drain drift-region formed in contact with the body region, the first trench side surface, and the trench bottom surface from the first corner portion to a first position;
• a second drain drift-region formed in contact with the trench bottom surface to extend from the first position in a direction of the second corner portion, and having an impurity concentration that is higher than an impurity concentration of the first drain drift-region;
• and
• a high-concentration drain region formed away from the body region, the first trench side surface, and the trench bottom surface, and having an impurity concentration higher than the impurity concentration of the second drain drift-region.