Zener diode with semiconductor region annularly surrounding anode

The semiconductor device includes a semiconductor layer having a main surface, a first semiconductor region of a first conductivity type formed in a surface layer portion of the main surface of the semiconductor layer, a second semiconductor region of a second conductivity type formed in a surface layer portion of the first semiconductor region and forming a zener diode with the first semiconductor region, a third semiconductor region of the first conductivity type formed in the surface layer portion of the first semiconductor region separated from the second semiconductor region, a fourth semiconductor region of the second conductivity type formed in a region between the second semiconductor region and the third semiconductor region in the surface layer portion of the first semiconductor region and having a second conductivity type impurity concentration less than a second conductivity type impurity concentration of the second semiconductor region, and an insulating layer formed on the main surface of the semiconductor layer and covering the second semiconductor region, the third semiconductor region and the fourth semiconductor region.