Semiconductor devices, and methods of fabricating the same, include first conductive lines on a substrate, and a first molding layer covering the first conductive lines. The first conductive lines have air gaps between adjacent first conductive lines. Sidewalls of the first conductive lines and a bottom surface of the first molding layer collectively define a first gap region of each of the air gaps. The sidewalls of the first conductive lines and a top surface of the first molding layer collectively define a second air gap region of each of the air gaps.