Methods of forming an interlayer dielectric having an air gap are provided including forming a first insulating layer on a semiconductor substrate. The first insulating layer defines a trench. A metal wire is formed in the trench such that the metal wire is recessed beneath an upper surface of the first insulating layer. A metal layer is formed on the metal wire, wherein the metal layer includes a capping layer portion filling the recess, a upper portion formed on the capping layer portion, and an overhang portion formed on the portion of the first insulating layer adjacent to the trench protruding sideward from the upper portion. The first insulating layer is removed and a second insulating layer is formed on the semiconductor substrate to cover the metal layer, whereby an air gap is formed below the overhang portion of the metal layer. A portion of the second insulating layer is removed to expose the upper portion of the metal layer. The upper portion and the overhang portion of the metal layer are removed. A third insulating layer is formed on the semiconductor substrate from which the upper portion and the overhang portion have been removed to maintain the air gap.