Semiconductor structures and fabrication methods are provided. An exemplary fabrication method includes providing a semiconductor substrate having a first region, a second region, a gate structure on the first region and a dummy gate structure on the second region, and an isolation structure in the semiconductor under the dummy gate structure. The method also includes forming source/drain openings in the semiconductor substrate at two sides of the gate structure. A sidewall surface of the source/drain opening contains an apex angle extending into the semiconductor substrate under the gate structure; and the source/drain opening exposes a sidewall surface of the isolation structure. Further; the method includes forming an initial bulk layer in the source/drain opening; performing a reshaping process to the initial bulk layer to form a bulk layer having an a substantially flat reshaped surface; and forming a protective layer on the bulk layer.