A semiconductor structure includes a substrate, at least one first gate structure, at least one first spacer, at least one source drain structure, at least one conductive plug, and at least one protection layer. The first gate structure is present on the substrate. The first spacer is present on at least one sidewall of the first gate structure. The source drain structure is present adjacent to the first spacer. The conductive plug is electrically connected to the source drain structure. The protection layer is present between the conductive plug and the spacer.