The present invention provides a method for forming a semiconductor structure, including: firstly, providing a substrate, a fin structure being disposed on the substrate, a gate structure crossing over the fin structure, and a first hard mask being disposed on the top surface of the gate structure. Next, a dielectric layer is formed, covering the substrate, the fin structure and the gate structure. Afterwards, a second hard mask is formed on the top surface of the first hard mask, where the width of the second hard mask is larger than the width of the first hard mask, a bottom surface of the second hard mask and a top surface of the first hard mask are on the same level. An etching process is then performed to remove parts of the dielectric and parts of the fin structure.