A method of fabricating a semiconductor device is provided. A plurality of first gate electrode structure is formed on a substrate. A recess is formed in the substrate, wherein the recess is formed between two adjacent first gate electrode structures of the plurality of first gate electrode structure. A diffusion prevention layer includes a first material and is formed on the recess of the substrate. A first pre-silicide layer includes a second material different from the first material and is formed on the diffusion prevention layer. A metal layer is formed on the first pre-silicide layer. The first pre-silicide layer and the metal layer are changed to a first silicide layer by performing an annealing process to the substrate. The diffusion prevention layer prevents metal atoms of the metal layer from diffusing to the substrate, and the first silicide layer comprises a monocrystalline layer.