A semiconductor device including a highly reliable transistor is provided. A semiconductor device includes a transistor. The transistor includes first and second gate electrodes, first and second gate insulators, a source electrode, a drain electrode, first to sixth oxides, first and second layers, and first and second gate insulators. The third oxide is under the source electrode. The fourth oxide is under the drain electrode. The sixth oxide is under the second gate electrode. The third and fourth oxides each have a function of supplying oxygen to the second oxide. The sixth oxide has a function of supplying oxygen to the second gate insulator.