A non-volatile memory device includes a set of memory cells, a cycle transistor, a reference transistor and a control circuit. The control circuit is coupled to the set of memory cells, the cycle transistor and the reference transistor. A method of controlling the non-volatile memory device includes in a program operation or an erase operation of the set of memory cells, the control circuit determining a state of the cycle transistor, and upon determining the cycle transistor being in an erased state (or a programmed state), the control circuit setting the reference transistor from a reference state to the erased state (or the programmed state), and then restoring the reference transistor from the erased state (or the programmed state) to the reference state. The reference state is set between the erased state and a programmed state.