Thereafter, by using the second resist pattern 62 as a mask, second ion beams 72 including boron (B) are ion implanted at acceleration energy of 50 keV and a dose of 1???1013 cm???2, thereby forming a first polarity inversion region 12A and a second polarity inversion region 12B both of the p-type conductivity within the respective p-type low concentration impurity regions 13 in the semiconductor