A method of fabricating a semiconductor device includes forming a first conductive structure over a substrate, successively forming a first spacer layer, a sacrificial layer, and a second spacer layer on the first conductive structure, forming a second conductive structure adjacent the first conductive structure and in contact with a lower portion of the second spacer layer, partially removing an upper portion of the second spacer layer to expose the sacrificial layer, removing the sacrificial layer through a vapor etch process to form an air gap between the lower portion of the second spacer layer and the first spacer layer, and forming a capping layer to cap the air gap.