A semiconductor device including a first fin protruding on a substrate and extending in a first direction; a first gate electrode on the first fin, the first gate electrode intersecting the first fin; a first trench formed within the first fin at a side of the first gate electrode; a first epitaxial layer filling a portion of the first trench, wherein a thickness of the first epitaxial layer becomes thinner closer to a sidewall of the first trench; and a second epitaxial layer filling the first trench on the first epitaxial layer, wherein a boron concentration of the second epitaxial layer is greater than a boron concentration of the first epitaxial layer.