Abstract: An oxide semiconductor device includes an oxide semiconductor transistor and a protection wall. The protection wall extends in a vertical direction and surrounds the oxide semiconductor transistor. The oxide semiconductor transistor includes a first oxide semiconductor layer, and a bottom surface of the protection wall is lower than the first oxide semiconductor layer in the vertical direction. In the oxide semiconductor device of the present invention, the protection wall is used to surround the oxide semiconductor transistor for improving the ability of blocking environment substances from entering the oxide semiconductor transistor. The electrical stability and product reliability of the oxide semiconductor device are enhanced accordingly.