THREE-DIMENSIONAL SEMICONDUCTOR DEVICE AND METHOD OF FABRICATING THE SAME

Disclosed are a three-dimensional semiconductor device and a method of fabricating the same. The semiconductor device includes: a first active region on a substrate, the first active region including a pair of lower source/drain regions and a lower channel structure; a second active region on the first active region, the second active region including a pair of upper source/drain regions and an upper channel structure; and a gate electrode on the lower and upper channel structures. The gate electrode includes: first and second metal structures, which are respectively provided adjacent bottom and top surfaces of semiconductor layers of the lower and upper channel structures.