A memory device includes a memory cell array having a plurality of memory strings and includes a voltage generating circuit configured to generate and apply a plurality of drain select line voltages, a plurality of source select line voltages, and a read voltage to the memory cell array during a read operation. The memory device also includes control logic configured to control the voltage generating circuit to generate a first drain select line voltage applied to a first unselected memory string among unselected memory strings among the plurality of memory strings and a second drain select line voltage applied to second unselected memory strings among the unselected memory strings during the read operation, wherein the second drain select line voltage is different from the first drain select line voltage.