A semiconductor device structure is provided. The semiconductor device structure includes a first fin structure and a second fin structure extending above an isolation structure. The semiconductor device structure includes a dummy fin structure formed over the isolation structure, and the dummy fin structure is between the first fin structure and the second fin structure. The semiconductor device structure includes a capping layer formed over the dummy fin structure, and the top surface of the capping layer is higher than the top surface of the first fin structure and the top surface of the second fin structure. The semiconductor device structure includes a first gate structure formed over first fin structure, and a second gate structure formed over the second fin structure. The first gate structure and the second gate structure are separated by the dummy fin structure and the capping layer.