A highly reliable semiconductor device with favorable electrical characteristics is provided. The semiconductor device includes a first insulator; a first conductor and a second conductor over the first insulator; an oxide provided between the first conductor and the second conductor; a second insulator over the first conductor, the second conductor, and the oxide; and a third conductor over the second insulator. A side surface of the first conductor includes a region in contact with one side surface of the oxide, a side surface of the second conductor includes a region in contact with the other side surface of the oxide. The level of a top surface of the first conductor, the level of a top surface of the second conductor, and the level of a top surface of the oxide are substantially the same. The conductivity of the first conductor is higher than that of the oxide, and the conductivity of the second conductor is higher than that of the oxide.