A memory device may include a selected bit line connected to a first node and configured to receive a first current, a selected memory cell connected to the selected bit line, a reference bit line connected to a second node and configured to receive a second current, a reference memory cell connected between the reference bit line and a reference source line, a sub bit line connected to the second node, a sub memory cell connected between the sub bit line and a sub source line, and a sense amplifier configured to sense a voltage difference between the first node and the second node to determine data read from a selected memory cell connected to the selected bit line. The sub memory cell may include a cell transistor. A gate electrode of the cell transistor may be connected to the sub source line.