a surface between gate electrodes in an mos gate structure is patterned so that missing portions are partially provided in surfaces of n + emitter regions to thereby enlarge surface areas of p + contact regions surrounded by the surfaces of the n + emitter regions . in this manner , a highly reliable mos type semiconductor device is provided which is improved in breakdown tolerance by suppressing an increase in the gain of a parasitic transistor caused by photo pattern defects produced easily in accordance with minute patterning in a process design rule .