A vertical NAND-type memory device includes a vertical stack of inter-gate insulating layers and gate electrodes arranged in an alternating sequence on an underlying substrate, which includes a cell array region and a contact region therein. At least one NAND-type channel structure is provided, which extends vertically through the vertical stack of inter-gate insulating layers and gate electrodes. An end sidewall of a first of the gate electrodes, which extends laterally over at least a portion of the contact region, has a vertical slope that is less steep than vertical slopes of end sidewalls of a first plurality of the gate electrodes extending between the first of the gate electrodes and the substrate.