A semiconductor structure is provided. The semiconductor structure includes nanostructures over a substrate, a gate stack around the nanostructures, a gate spacer layer alongside the gate stack, an inner spacer layer between the gate spacer layer and the nanostructures, a source/drain feature adjoining the nanostructures, a contact plug over the source/drain feature, and a silicon germanium layer along the surface of the source/drain feature and between the contact plug and the inner spacer layer.