A semiconductor device includes first and second bit line structures on a substrate and spaced apart from each other, a via plug partially filling between the first and second bit line structures, a via pad in contact with an upper surface of the via plug and an upper sidewall of the first bit line structure, the via pad being spaced apart from an upper portion of the second bit line structure, a first cavity filled with air being between the via plug and the first bit line structure and a second cavity filled with air between the via plug and the second bit line structure, A gap capping spacer having a first portion on the upper sidewall of the first bit line structure and a second portion covers the first air spacer. A horizontal width of the first portion is smaller than that of the second portion.