PURPOSE: To obtain a Zener diode with high stability, by providing a peak density profile with the width corresponding to the fluctuation width of the density profile on an N+ type diffused region which is crossed therewith.

CONSTITUTION: When forming the P+ type diffused region 3, a plurality of times of boron impurity ion implantations are performed. The peak density of elongation-diffused impurity after an implantation is evenly formed by varying an implantation energy of each time and controlling a dope amount. In this process, the impurity density profile of the P+ type region is formed in a trapezoid, and the diffusion depth for the N+ type diffused region 4 is set to the central depth of the trapezoidal part. Thereby, the fluctuation of a breakdown voltage due to the dispersion of the P type impurity density or diffusion depth can be reduced.