According to an example embodiment, a method of operating a semiconductor device having a variable resistance device includes: applying a first voltage to the variable resistance device to change a resistance value of the variable resistance device from a first resistance value to a second resistance value that is different from the first resistance value; sensing a first current flowing through the variable resistance device to which the first voltage is applied; determining a second voltage used for changing the variable resistance device from the second resistance value to the first resistance value, based on a dispersion of the sensed first current; and applying the determined second voltage to the variable resistance device.