A data driver includes: a signal generator which includes a staircase waveform gray voltage signal generator which generate a plurality of staircase waveform gray voltage signals using a lowest gamma reference voltage, a highest gamma reference voltage, and a plurality of gamma voltages having a magnitude between the lowest gamma reference voltage and the highest gamma reference voltage; and a channel driver which includes a decoder which output one staircase waveform gray voltage signal selected from the staircase waveform gray voltage signals, an output circuit which output a gray voltage corresponding to the selected staircase waveform gray voltage signal, and a reset unit which supplies one of the gamma voltages to the output circuit as a reset voltage.