An integrated circuit device includes an electrically conductive pattern on a substrate. This electrically conductive pattern may be a gate pattern of a field effect transistor. A first electrically insulating spacer is provided on a sidewall of the electrically conductive pattern. The first electrically insulating spacer includes a first lower spacer and a first upper spacer, which extends on the first lower spacer and has a side surface vertically aligned with a corresponding side surface of the first lower spacer. The first upper spacer has a greater dielectric constant relative to a dielectric constant of the first lower spacer. A pair of parallel channel regions may also be provided, which protrude from a surface of the substrate. The electrically conductive pattern may surround top and side surfaces of the pair of parallel channel regions.