A data output buffer includes an output terminal, a buffer and a pull-down driver. The output terminal is coupled to a first end of a transmission line, the transmission line being coupled to a pull-up termination resistor at a second end. The buffer pulls up the output terminal to a first power supply voltage and pulls down the output terminal to a second power supply voltage based on an output data signal. The pull-down driver pre-emphasizes an initial stage of a pull-down driving operation of the output terminal based on the output data.