A memory device includes a memory cell region including a first metal pad, a peripheral circuit region including a second metal pad and connected to the memory cell region by the first and second metal pads, and a memory cell array in the memory cell region and including cell strings. The cell strings include memory cells, word lines and dummy lines connected to the memory cells, bit lines connected to one side of the cell strings, and a ground selection line connected to the cell strings. The memory device further includes control logic in the peripheral circuit region and including a precharge control circuit that controls a precharge on partial cell strings among the cell strings and controls data program steps on the memory cells, and a row decoder in the peripheral circuit region that activates at least some of the word lines based on control of the control logic.