A wiring structure of a semiconductor device may have an insulation layer, a spacer and a plug. The insulation layer may be provided on a substrate and may have an opening through which a contact region of the substrate is exposed. The spacer may be provided on a sidewall of the opening. The plug may fill the opening and may include a polysilicon pattern doped with impurities, a metal silicide pattern, and a metal pattern sequentially provided on the substrate.