There is improved performance of a semiconductor device including a fin-type low-withstand-voltage transistor and a fin-type high-withstand-voltage transistor. A low-withstand-voltage transistor is formed on each of a plurality of first fins isolated from each other by a first element isolation film, and a high-withstand-voltage transistor, which has a channel region including tops and side surfaces of a plurality of second fins and a top of a semiconductor substrate between the second fins adjacent to each other, is formed. At this time, a top of a second element isolation film surrounding the second fins including part of the channel region of one high-withstand-voltage transistor is lower than a top of the first element isolation film.