A semiconductor device and a method for operating the same includes a first P-type semiconductor layer and a first N-type semiconductor layer provided thereon. A plurality of second P-type semiconductor layers and a plurality of third P-type semiconductor layers are formed on the surface of the first N-type semiconductor layer. A plurality of second N-type semiconductor layers are formed on their respective surfaces of the third P-type semiconductor layers. Emitter electrodes are provided on the second P-type semiconductor layers and second N-type semiconductor layers. A plurality of first gate electrodes is each provided above the first N-type semiconductor layer between the adjacent third P-type semiconductor layers. A plurality of second gate electrodes are each provided above the first N-type semi-conductor layer between the second P-type semiconductor layer and the third P-type semiconductor layer. A collector electrode is provided under the first P-type semiconductor layer. If the timing at which a bias is applied to the first gate electrodes and second gate electrodes is controlled, an operation mode in which the device serves as a thyristor and an operation mode in which the device serves as an IGBT can be switched to each other. Therefore, the semiconductor device, which can be turned on/turned off, is capable of being turned off at high speed when an on-state voltage is low.