A semiconductor device including a semiconductor substrate having a first conductive type layer; a first diffusion region which has the first conductive type and is formed in the first conductive type layer; a second diffusion region which has a second conductive type and an area larger than an area of the first diffusion region and overlaps the first diffusion region; and a PN junction formed at an interface between the first and the second diffusion regions. The second diffusion region includes a ring shaped structure or a guard ring includes an inverted region which has the second conductive type. According to such a configuration, it is possible to provide a semiconductor device having the required Zener characteristics with good controllability.