Patent ID: 8093622

Claim:
A method for driving a semiconductor device, comprising: providing a device including: an n-type semiconductor layer formed on a substrate; an n-type well region of higher n-type impurity concentration than the semiconductor layer formed in a top portion of the semiconductor layer; a p-type well region formed in the top portion of the semiconductor layer laterally spaced from the n-type well region; a first p-type contact region formed in a top portion of the n-type well region; a first n-type contact region of different n-type impurity concentration than the n-type well region formed in the top portion of the n-type well region laterally spaced from the first p-type contact region; a second p-type contact region of higher p-type impurity concentration than the p-type well region formed in a top portion of the p-type well region; a second n-type contact region formed in the top portion of the p-type well region laterally spaced from the second p-type contact region; and a gate defined by a gate insulating film and a gate electrode formed over the p-type well region at least from an interface of the p-type well region with the second n-type contact region to an interface of the p-type well region with the semiconductor layer; wherein the first p-type contact region, the n-type well region, the n-type semiconductor layer, the p-type well region and the second n-type contact region form a thyristor with an anode at the first p-type contact region, a cathode at the second n-type contact region, an anode gate at the first n-type contact region, and a cathode gate at the second p-type contact region; and the second n-type contact region, the n-type semiconductor layer 20 and the p-type well region under the gate define source, drain and channel regions of a MOS transistor; turning the thyristor from an “off” state to an “on” state by first applying an “on” potential to the gate electrode to turn the MOS transistor “on”, thereby lowering a potential at the anode gate to below a potential at the anode and forward biasing a diode comprising the anode and anode gate; and then, with the “on” potential still applied to the gate electrode, setting a potential at the cathode gate to a higher potential than the cathode, thereby flowing current between the anode and cathode; and turning the thyristor from an “on” state to an “off” state by first applying a potential to the anode gate to set the potential of the semiconductor layer to a higher potential than the anode to reverse bias the diode; and thereafter reducing the potential set at the cathode gate to the same potential as the cathode.