SEMICONDUCTOR DEVICE

PROBLEM TO BE SOLVED: To increase a switching speed in turn-off.SOLUTION: A semiconductor device comprises a separation insulation film 8 arranged in each trench for dividing a gate electrode 7 into a first gate electrode 7a located on an opening side of the trench 5 and a second gate electrode 7b located on a bottom side of the trench 5 so as to enable independent control over the first and second gate electrodes 7a, 7b from each other. When electrical continuity is established, a voltage is applied to the first gate electrode 7a so as to form an inversion layer 14 in a base layer 4 at a part which contacts a gate insulation film 6 under the first gate electrode 7a, and a voltage is applied to the second gate electrode 7b so as to form an accumulation layer 15 in a drift layer 3 at a part which contacts the gate insulation film 6 under the second gate electrode 7b. When the semiconductor device is turned off, a voltage is applied to the second gate electrode 7b so as to vanish the accumulation layer 15 and subsequently, a voltage is applied to the first gate electrode 7a after the elapse of a predetermined period of time so as to vanish the inversion layer 14.