Semiconductor devices are provided including an active pillar protruding from a substrate; a first gate electrode and a second gate electrode adjacent to a sidewall of the active pillar and vertically overlapping with each other, the first and second gate electrodes being insulated from each other; a first intergate insulating layer covering a first surface of the first gate electrode; and a second intergate insulating layer covering a second surface, opposite the first surface, of the second gate electrode and spaced apart from the first intergate insulating layer. The first intergate insulating layer and the second intergate insulating layer define an air gap therebetween.