An improvement is achieved in the performance of a semiconductor device. A semiconductor device includes an n−-type semiconductor region formed in a p-type well, an n-type semiconductor region formed closer to a main surface of a semiconductor substrate than the n−-type semiconductor region, and a p−-type semiconductor region formed between the n−-type semiconductor region and the n-type semiconductor region. A net impurity concentration in the n−-type semiconductor region is lower than a net impurity concentration in the n-type semiconductor region. A net impurity concentration in the p−-type semiconductor region is lower than a net impurity concentration in the p-type well.