10 is arranged on the exposed surface of the n 3 layer 6 which constitutes the auxiliary thyristor s so as not to be short circuited to the p 2 layer 4 and the external resistor 15 is connected between the metallic layer 8 arranged on the p 2 layer 4 and the electrode 10 the diode 16 is interposed between the cathode electrode assembly k and the electrode 10 to prevent a current from flowing from the n 3 layer 6 to the cathode electrode assembly k of the main thyristor portion m a control electrode member is formed by the first gate electrode assembly g 1 and the second gate electrode assembly g 2 a main electrode is comprised by the anode electrode assembly a and the cathode electrode assembly k a bias control member includes the control power 13 the switch element 14 the resistor 15 and the diode 16 a device of the kind described above was made essentially as follows first an n type silicon wafer having resistivity of the order of 50 60 u03c9 cm was prepared the layers p 1 n 1 and p 2 were formed by diffusing gallium at a temperature of about 1250 u00b0 c by a closed tube diffusion method in this case the diffusion depths that is the thicknesses of the p 1 layer and p 2 layer were 50 u03bcm and the surface densities of the p 1 layer and p 2 layer were of the order of 1 u00d7 10 18 atoms cm 3 oxide films.