A semiconductor device includes a substrate, a semiconductor channel layer, a semiconductor barrier layer, a gate electrode, a first electrode, a second electrode, a first dielectric layer and a second dielectric layer. The semiconductor channel layer is disposed on the substrate. The semiconductor barrier layer is disposed on the semiconductor channel layer. The gate electrode is disposed on the semiconductor barrier layer. The first electrode is disposed at one side of the gate electrode. The first electrode includes a body portion and a vertical extension portion. The second electrode is disposed at another side of the gate electrode. The second electrode includes a body portion and a vertical extension portion. The first dielectric layer is disposed between the vertical extension portion of the first electrode and the semiconductor channel layer. The second dielectric layer is disposed between the vertical extension portion of the second electrode and the semiconductor channel layer.