| A semiconductor structure includes a substrate, a channel layer, a barrier layer, a gate structure, a first passivation layer and a second passivation layer. The channel layer is disposed on the substrate. The barrier layer is disposed on the channel layer. The gate structure and the first passivation layer are disposed on the barrier layer. The second passivation layer is disposed on the first passivation layer, and a material composition of the second passivation layer is different from a material composition of the first passivation layer. The channel layer has two first two-dimensional electron gas regions near the barrier layer, and the two first two-dimensional electron gas regions are respectively located on two sides of the gate structure. The barrier layer has two second two-dimensional electron gas regions near the first passivation layer, and the two second two-dimensional electron gas regions are respectively located on two sides of the gate structure. Therefore, the semiconductor structure can have enhancement-mode and dual-channel effects. |