Semiconductor devices may include a diffusion prevention insulation pattern, a plurality of conductive patterns, a barrier layer, and an insulating interlayer. The diffusion prevention insulation pattern may be formed on a substrate, and may include a plurality of protrusions protruding upwardly therefrom. Each of the conductive patterns may be formed on each of the protrusions of the diffusion prevention insulation pattern, and may have a sidewall inclined by an angle in a range of about 80 degrees to about 135 degrees to a top surface of the substrate. The barrier layer may cover a top surface and the sidewall of each if the conductive patterns. The insulating interlayer may be formed on the diffusion prevention insulation pattern and the barrier layer, and may have an air gap between neighboring ones of the conductive patterns.