The present invention provides a semiconductor device including a semiconductor substrate, a first well, a second well, a gate electrode, an oxide semiconductor structure and a diode. The first well is disposed in the semiconductor substrate and has a first conductive type, and the second well is also disposed in the semiconductor substrate, adjacent to the first well, and has a second conductive type. The gate electrode is disposed on the first well. The oxide semiconductor structure is disposed on the semiconductor substrate and electrically connected to the second well. The diode is disposed between the first well and the second well.