A semiconductor structure including a semiconductor substrate is provided. The semiconductor substrate includes a surface. A gate structure is provided on the surface. An interface lower than the surface is provided. An epitaxial regrowth region adjacent the gate structure is disposed on the interface. In addition, the epitaxial regrowth region extends over the surface and includes a bottom layer and a cap layer. The activation of the cap layer is lower than that of the bottom layer. Moreover, the bottom layer is lower than the surface and the gate structure. Furthermore, the bottom layer includes a first downwardly-curved edge and a second downwardly-curved edge over the first one. The first downwardly-curved edge is connected with the second downwardly-curved edge at two endpoints. The two endpoints are in contact with the surface of the semiconductor substrate.