A semiconductor memory device includes: a semiconductor region extending vertically from a first region of a substrate; a plurality of gate electrodes disposed on the first region of the substrate in a vertical direction, but separated from each other along a sidewall of the semiconductor region; a gate dielectric layer disposed between the semiconductor region and the plurality of gate electrodes; a substrate contact electrode extending vertically from the impurity-doped second region of the substrate; and an insulating region formed as an air gap between the substrate contact electrode and at least one of the plurality of gate electrodes.