A method of repairing a memory device is provided. If an erase process is unsuccessful, a repair process is performed. A programmed state of the memory device is determined, A subsequent erase process dependent on the programmed state is performed. Also, a method of programming and erasing a memory device is provided. The memory device includes first and second electrodes and a switching layer therebetween. A first on-state resistance characteristic of the memory device is provided in programming the memory device by application of a first voltage to the gate of a transistor in series with the memory device. Other on-state resistance characteristics of the memory device, different from the first on-state resistance characteristic, may be provided by application of other voltages, different from the first voltage, to the gate of the transistor.