a semiconductor device is composed a semiconductor substrate having a first conducting - type first semiconductor layer , a second conducting - type second semiconductor layer , a first conducting - type third semiconductor layer , a second conducting - type fourth semiconductor layer and a first conducting - type fifth semiconductor layer , a first main electrode for short - circuiting the first semiconductor layer and the second semiconductor layer , a second main electrode for short - circuiting the fourth semiconductor layer and the fifth semiconductor layer , and a control electrode provided on the third semiconductor layer . the first semiconductor layer and the second semiconductor layer form a joint . the second semiconductor layer and the third semiconductor layer form a joint . the third semiconductor layer and the fourth semiconductor layer form a joint . the fourth semiconductor layer and the fifth semiconductor layer form a joint .