A transistor with favorable electrical characteristics is provided. A minute transistor is provided. Provided is a semiconductor device including a first insulator over a substrate, a second insulator over the first insulator, a semiconductor over the second insulator, a first conductor and a second conductor over the semiconductor, a third insulator over the semiconductor, a fourth insulator over the third insulator, a third conductor over the fourth insulator, and a fifth insulator over the first insulator, the first conductor, and the second conductor. In the semiconductor device, the second insulator and the third insulator each include at least one element other than oxygen included in the semiconductor, respectively, and the semiconductor includes a region having a carbon concentration of 3×1018 atoms/cm3 or lower.