An example memory device includes a first
wafer that includes a first sub-
memory block connected to first to n-th word lines, a first
bit line, a first string selection line, and a first ground selection line, and a second
wafer that is stacked on the first
wafer in a vertical direction and includes a second sub-
memory block connected to (n+1)-th to 2n-th word lines, a second
bit line, a second string selection line, and a second ground selection line. The first to n-th word lines are respectively connected to the (n+1)-th to 2n-th word lines and share first to n-th word line drivers with the (n+1)-th to 2n-th word lines. The first
bit line is connected to the second bit line and shares a first page buffer with the second bit line.