A semiconductor device is provided, which includes an active structure, a first semiconductor layer, a second semiconductor layer, an intermediate layer, a transition layer and a contact layer. The active structure has two sides and includes an active region. The first semiconductor layer and the second semiconductor layer respectively located on the two sides of the active structure. The intermediate layer is located between the second semiconductor layer and the active structure. The transition layer is located on the second semiconductor layer. The contact layer is located on the transition layer.