A word line driver for use in a semiconductor memory device includes a boosted voltage generator, a sub word line driver and a main word line driver. The boosted voltage generator generates a boosted voltage by receiving an internal power supply voltage and pumping electric charge. The sub word line driver receives the internal power supply voltage and activates a boosted voltage control signal after supplying the internal power supply voltage to a boost node in a command operating mode. The main word line driver enables a word line by supplying the boosted voltage to the boost node in response to the boosted voltage control signal in a normal operating mode, and enables the word line with the boosted voltage after boosting the word line to the internal power supply voltage by changing the boost node from the internal power supply voltage to the boosted voltage in the command operating mode.