Semiconductor memory devices and memory systems including the same

A semiconductor memory device includes a memory cell array, sub word-line drivers and power selection switches. The memory cell array includes memory cell rows coupled to word lines. The sub word line drivers are coupled to the word lines. The power selection switches are coupled to the sub word-line drivers. Each power selection switch controls a deactivation voltage level of a first word-line activated from the word-lines and an off-voltage level of a second word line adjacent to the first word line so that the deactivation voltage level and the off-voltage level have at least one of a ground voltage, a first negative voltage and a second negative voltage. The ground voltage, the first negative voltage and the second negative voltage have different voltage levels from each other.