The semiconductor device of the present invention has a repeat structure of repeated unit structures in a semiconductor substrate (1), each unit structure having an n type diffusion region (3) and a p type diffusion region (4) in contact with each other to form a pn junction sandwiched between trenches (1a). An impurity amount in the n type diffusion region (3) and an impurity amount in the p type diffusion region (4) in the unit structure are set unequal (or different). Thus, in the semiconductor device having the trenches (1a), favorable breakdown voltage and avalanche breakdown tolerance can be ensured at the same time.