A gate-all-around structure is provided. The gate-all-around structure includes a plurality of nanostructures stacked over a substrate in a vertically direction, and the nanostructures extends from a gate region to a source/drain (S/D) region. The gate-all-around structure includes a gate structure formed in the gate region around the first nanostructures, and a S/D structure formed in the S/D region. The S/D structure is in direct contact with a top surface of one of the nanostructures.