A semiconductor device includes a semiconductor pattern on a substrate, gate structures on sidewalls of the semiconductor pattern, the gate structures being spaced apart from one another, insulating interlayers among the gate structures, wherein an uppermost insulating interlayer is lower than an upper face of the semiconductor pattern, a common source line contacting the substrate and protruding above the uppermost insulating interlayer, an etch stop layer pattern on the semiconductor pattern and on the common source line wherein the common source line protrudes above the uppermost insulating interlayer, an additional insulating interlayer on the uppermost insulating interlayer, and contact plugs extending through the additional insulating interlayer so as to make contact with the semiconductor pattern and the common source line, respectively.