A memory device includes a memory cell region including a first metal pad, a peripheral circuit region including a second metal pad and vertically connected to the memory cell region by the first and second metal pads, a memory cell array in the memory cell region including cell strings including memory cells, word lines respectively 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, a control logic in the peripheral circuit region including a precharge control circuit for controlling precharge on partial cell strings among the cell strings and controlling a plurality of data program steps on the memory cells, and a row decoder in the peripheral circuit region for activating at least some of the word lines in response to a control of the control logic.