Semiconductor structures are provided. The semiconductor structure includes a fin structure protruding from a substrate and a doped region formed in the fin structure. The semiconductor structure further includes a metal gate structure formed across the fin structure and a gate spacer formed on a sidewall of the metal gate structure. The semiconductor structure further includes a source/drain structure formed over the doped region. In addition, the doped region continuously surrounds the source/drain structure and is in direct contact with the gate spacer.