A semiconductor integrated circuit includes: a p−-type semiconductor substrate defining a high-potential side circuit area and a low-potential side circuit area separated from each other; a high-side n well provided in an upper part of the semiconductor substrate in the high-potential side circuit area; a high-side p well provided in the high-side n well; and a p-type semiconductor region provided in an upper part of the semiconductor substrate in the low-potential side circuit area; and n+-type semiconductor region provided to be brought contact with the p-type semiconductor region, wherein a whole n-type semiconductor region including the n+-type semiconductor region, has an impurity concentration higher than an impurity concentration of the high-side n well.