Insulated-gate semiconductor device and method of manufacturing the same

A method of manufacturing an insulated-gate semiconductor device, includes: digging a gate trench and a dummy trench; burying a dummy electrode in the dummy trench via a gate insulating film and burying a gate electrode in the gate trench via the gate insulating film; exposing an upper portion of the dummy electrode and selectively forming an insulating film for testing so as to cover the gate electrode; depositing a conductive film for testing on the dummy electrode and the insulating film for testing; and selectively testing an insulating property of the gate insulating film in the dummy trench by applying a voltage between the conductive film for testing and the charge transport, region.