Abstract: An output buffer circuit for reducing a variation of the slew rate due to a variation of process, voltage and temperature (PVT) and the load capacitance of an output terminal, and semiconductor device including the same, include a first slew rate control circuit for pulling down the voltage of a pull-up signal in multiple stages in response to a first control signal, and a second slew rate control circuit for pulling up the voltage of a pull-down signal in multiple stages in response to a second control signal. A pull-up driver is provided for pulling up an output terminal in response to the pull-up signal, and a pull-down driver is provided for pulling down the output terminal in response to the pull-down signal. The first and second slew rate control circuits are controlled by bias voltages that are provided by a phase locked loop circuit and compensate for changes in PVT.