A minute transistor is provided. A semiconductor device includes a semiconductor over a substrate, a first conductor and a second conductor over the semiconductor, a first insulator over the first conductor and the second conductor, a second insulator over the semiconductor, a third insulator over the second insulator, and a third conductor over the third insulator. The third insulator is in contact with a side surface of the first insulator. The semiconductor includes a first region where the semiconductor overlaps with a bottom surface of the first conductor, a second region where the semiconductor overlaps with a bottom surface of the second conductor, and a third region where the semiconductor overlaps with a bottom surface of the third conductor. The length between a top surface of the semiconductor and the bottom surface of the third conductor is longer than the length between the first region and the third region.