A semiconductor device includes a first electrode, a first insulating layer having a first opening reaching the first electrode and having a ring-shaped first side wall exposed to the first opening, an oxide semiconductor layer on the first side wall, the oxide semiconductor layer being connected with the first electrode, a gate insulating layer on the oxide semiconductor layer, the oxide semiconductor layer being between the first side wall and the gate insulating layer, a gate electrode facing the oxide semiconductor layer on the first side wall, the gate insulating layer being between the oxide semiconductor layer and the gate electrode, and a second electrode above the first insulating layer, the second electrode being connected with the oxide semiconductor layer.