Methods for forming semiconductor structures are provided. The method includes alternately stacking first semiconductor layers and second semiconductor layers over a substrate and patterning the first semiconductor layers and the second semiconductor layers to form a first fin structure. The method further includes forming a first trench in the first fin structure and forming a first source/drain structure in the first trench. The method further includes partially removing the first source/drain structure to form a second trench in the first source/drain structure and forming a first contact in the second trench.