Insulated-gate semiconductor device and method of manufacturing the same

A method of manufacturing an insulated-gate semiconductor device, comprising:

• forming an injection control region of a second conductivity-type on a charge transport region of a first conductivity-type;
• forming a main charge supply region of the first conductivity-type on the injection control region;
• digging a dummy trench so as to penetrate the main charge supply region and the injection control region to reach the charge transport region, and digging a gate trench so as to have a U-like shape in a planar pattern adjacent to the dummy trench to surround the dummy trench into the U-like shape;
• burying a conductive film in the dummy trench via a gate insulating film to serve as a dummy electrode, and burying a conductive film in the gate trench via the gate insulating film to serve as a gate electrode;
• forming a projection for testing connected to the dummy electrode via an opening of the U-like shape, and forming a wiring layer for testing connected to the projection for testing;
• and
• testing an insulating property of the gate insulating film in the dummy trench by applying a voltage between the wiring layer for testing and a bottom surface of the charge transport region.