A three-dimensional semiconductor device includes a first channel pattern on and spaced apart from a substrate, the first channel pattern having a first end and a second end that are spaced apart from each other in a first direction parallel to a top surface of the substrate, and a first sidewall and a second sidewall connecting between the first end and the second end, the first and second sidewalls being spaced apart from each other in a second direction parallel to the top surface of the substrate, the second direction intersecting the first direction, a bit line in contact with the first end of the first channel pattern, the bit line extending in a third direction perpendicular to the top surface of the substrate, and a first gate electrode adjacent to the first sidewall of the first channel pattern.