Semiconductor device and protection method

摘要

A semiconductor device comprises a main switching element, an electric field detector (20a) and an on-voltage application unit (Rg). The main switching element includes a high-voltage main electrode (12), at least a low-voltage main electrode (18) and at least a first gate electrode (17). The electric field detector has a MOS structure (22, 26, 27) making conductive between the high-voltage main electrode and the first gate electrode in a path other than the main switching element in accordance with a predetermined electric field generated in the main switching element. The on-voltage application unit applies an on-voltage to the first gate electrode on the basis of the conductive state.