Semiconductor device

A semiconductor device, comprising:

• a semiconductor substrate of a first conductivity type;
• a semiconductor layer of the first conductivity type formed on the semiconductor substrate;
• a base layer of a second conductivity type formed in a surface of the semiconductor layer;
• a gate insulator formed on sidewalls of each of a plurality of trenches formed through the base layer;
• a bottom insulator formed at a bottom of each of the trenches and extending through the semiconductor layer and into the semiconductor substrate;
• a gate electrode provided in each of the trenches and insulated from the semiconductor substrate, semiconductor layer and base layer by the bottom and gate insulators;
• source regions of the first conductivity type formed in a surface of the base layer;
• contact regions of the second conductivity type formed in the surface of the base layer;
• the bottom insulator having a thickness extending between the semiconductor substrate and the gate electrode,
• the gate insulator having a thickness extending between the base layer and the gate electrode,
• the thickness of the bottom insulator being greater than the thickness of the gate insulator,
• the adjacent two of the trenches each having a width greater than a distance between the adjacent two trenches.