A semiconductor device includes a semiconductor structure, a plurality of gate structures, at least one source/drain structure, at least one trench, a dielectric pattern, and a conductive structure. The gate structures are disposed on the semiconductor structure. The source/drain structure is disposed between two adjacent gate structures. The trench is disposed between the two adjacent gate structures and corresponding to the source/drain structure. The dielectric pattern is disposed on sidewalls of the trench. The conductive structure is disposed in the trench and electrically connected to the source/drain structure. The conductive structure includes a first portion surrounded by the dielectric pattern and a second portion connected to the source/drain structure, and the first portion is disposed on the second portion. A width of the first portion is smaller than a width of the second portion.