Semiconductor device

A semiconductor device comprising:

• a semiconductor base body including a substrate of a first conductivity type and a first semiconductor layer of a second conductivity type that is over the substrate;
• a first electrode over the semiconductor base body, the first electrode contacting the semiconductor base body;
• a second electrode over the semiconductor base body, the second electrode being spaced apart from the first electrode, the second electrode contacting the semiconductor base body;
• an isolation film over a surface of the semiconductor base body in a region between the first electrode and the second electrode;
• an insulation film over the surface of the semiconductor base body in a region between the second electrode and the isolation film;
• and
• a third electrode over the insulation film, wherein the first electrode is configured to electrically connect to a first circuit and to a first power source,
• the second electrode is configured to electrically connect to a second circuit and to a second power source, and
• the semiconductor base body further includes
• a back gate region of a conductivity type which is of the same conductivity type as that of the substrate, in at least a region of the semiconductor base body that faces the third electrode through the insulation film, and the back gate region at least in the region having a depth reaching the substrate, a dopant concentration of the back gate region falling within a range of 1×1010 cm−3 to 1×1015 cm−3.