A semiconductor structure includes a substrate, a first gate structure, a first spacer, a source drain structure, a first dielectric layer, a conductor, and a protection layer. The first gate structure is present on the substrate. The first spacer is present on a sidewall of the first gate structure. The source drain structure is present adjacent to the first spacer. The first dielectric layer is present on the first gate structure and has an opening therein, in which the source drain structure is exposed through the opening. The conductor is electrically connected to the source drain structure, in which the conductor has an upper portion in the opening of the first dielectric layer and a lower portion between the upper portion and the source drain structure. The protection layer is present between the lower portion and the first spacer and between the upper portion and the source drain structure.