A semiconductor device and a method of manufacturing a semiconductor device, the device including a first semiconductor pattern on a substrate, the first semiconductor pattern including a lower channel; a second semiconductor pattern on the first semiconductor pattern and spaced apart from the first semiconductor pattern in a vertical direction, the second semiconductor pattern including an upper channel extending in the vertical direction; a gate electrode covering the lower channel and surrounding the upper channel; and source/drain patterns on opposite sides of the upper channel, wherein the substrate and the first semiconductor pattern have a doping concentration of 1019/cm3 or less.