A memory device includes a set of memory cells, each of which is capable of being selected to generate a sensing current depending on a logic state thereof, and a set of reference cells, each of which is capable of being selected to generate a reference current. A sense amplifier is coupled to the memory cells and the reference cells for comparing the sensing current with the reference current to generate a signal representing the logic state of the selected memory cell. The memory cells and the reference cells are subject to the same operation cycles, such that a difference between the sensing current and the reference current remains a constant.