A semiconductor device includes a doped substrate, a barrier layer, a channel layer, and a doped semiconductor structure. The barrier layer is disposed on the doped substrate. The channel layer is disposed between the doped substrate and the barrier layer, in which a bandgap of the barrier layer is greater than a bandgap of the channel layer. The doped semiconductor structure is embedded in the doped substrate and at a position lower than the channel layer, in which the doped substrate and the doped semiconductor structure have different polarities, so as to form a diode therebetween.