A memory device includes a lower structure and a plurality of upper structures stacked on the lower structure. The lower structure includes a peripheral circuit, and an upper bonding pad disposed on a top surface of the lower structure. Each of the plurality of upper structures includes a bit line, a through via, and a lower bonding pad disposed on a bottom surface of the upper structures and connected to the through via. Each of upper structures, other than an uppermost upper structure, further includes an upper bonding pad disposed on a top surface thereof and connected to the through via. The bit line includes a gap separating a first portion of the bit line from a second portion thereof in the horizontal direction, and the through via overlaps the gap of the bit line in a plan view.