A memory device may include a peripheral region and a cell region. The peripheral region may include a first substrate, a plurality of circuit elements disposed on the first substrate, a first insulating layer disposed on the plurality of circuit elements, and a first protective layer disposed in the first insulating layer. The cell region may include a second substrate disposed on the first insulating layer, wherein the ceil region includes a first impurity region, a channel region extending in a direction substantially perpendicular to an upper surface of the second substrate, a plurality of gate electrode layers stacked on the second substrate and adjacent to the channel region, and a first contact electrically connected to the first impurity region, wherein the first protective layer is disposed below the first impurity region, and has a shape corresponding to a shape of the first impurity region.