A 3D semiconductor device and a method of manufacturing the same are provided. The 3D semiconductor device includes a semiconductor substrate, a common source region formed on the semiconductor substrate and extending in a line shape, an active region formed on the common source region and including a lateral channel region, which is substantially in parallel to a surface of the semiconductor substrate, and source and drain regions that are branched from the lateral channel region to a direction substantially perpendicular to the surface of the semiconductor substrate, and a gate formed in a space between the source region and the drain region.