In a semiconductor device 100, a light emitting element 120 has been mounted on an upper plane of a semiconductor substrate 102. In an impurity diffusion region of the semiconductor substrate 102, a P conducting type of a layer 104, and an N layer 106 have been formed, while an N conducting type impurity is implanted to the P layer 104, and then the implanted impurity is diffused to constitute the N layer 106. A zener diode 108 made of a semiconductor device has been formed by the P layer 104 and the N layer 106.