A semiconductor device is provided, including a substrate, a seed layer on the substrate, an epitaxial layer on the seed layer, an electrode structure on the epitaxial layer and an electric field modulation structure. The electrode structure includes a gate structure, a source structure and a drain structure, wherein the source structure and the drain structure are positioned on opposite sides of the gate structure. The electric field modulation structure includes an electric connection structure and a conductive layer electrically connected to the electric connection structure. The conductive layer is positioned between the gate structure and the drain structure. The electric connection structure is electrically connected to the source structure and the drain structure.