A semiconductor device with high reliability is provided. The semiconductor device includes a first insulator, a second insulator, and a transistor; the transistor includes an oxide in a channel formation region; the oxide is surrounded by the first insulator; and the first insulator is surrounded by the second insulator. The first insulator includes a region with a lower hydrogen concentration than the second insulator. Alternatively, the first insulator includes a region with a lower hydrogen concentration than the second insulator and with a lower nitrogen concentration than the second insulator.