Void boundary structures, semiconductor devices having the void boundary structures, and methods of forming the same are provided. The structures, semiconductor devices and methods present a way for reducing parasitic capacitance between interconnections by forming a void between the interconnections. The interconnections may be formed on a semiconductor substrate. An upper width of each of the interconnections may be wider than a lower width thereof. A molding layer encompassing the interconnections may be formed. A void boundary layer covering the molding layer may be formed to define the void between the interconnections.