A minute transistor is provided. A transistor with low parasitic capacitance is provided. A transistor having high frequency characteristics is provided. A semiconductor device including the transistor is provided. A semiconductor device includes an oxide semiconductor, a first conductor, a second conductor, a third conductor, a first insulator, and a second insulator. The first conductor overlaps with the oxide semiconductor with the first insulator positioned therebetween. The second insulator has an opening and a side surface of the second insulator overlaps with a side surface of the first conductor in the opening with the first insulator positioned therebetween. Part of a surface of the second conductor and part of a surface of the third conductor are in contact with the first insulator in the opening. The oxide semiconductor overlaps with the second conductor and the third conductor.