The present invention provides a semiconductor structure, including a substrate, having a fin structure disposed thereon, a gate structure, crossing over parts of the fin structure. The top surface of the fin structure which is covered by the gate structure is defined as a first top surface, and the top surface of the fin structure which is not covered by the gate structure is defined as a second top surface. The first top surface is higher than the second top surface, and a spacer covers the sidewalls of the gate structure. The spacer includes an inner spacer and an outer spacer, and the outer pacer further contacts the second top surface of the fin structure directly.