in a semiconductor device , an input buffer for buffering an input signal to provide an internal signal includes a reference voltage adjusting unit configured to receive a reference voltage and to output a first reference signal having a potential level higher than that of the reference voltage and a second reference signal having a potential level lower than that of the reference voltage , a multiplexing unit configured to selectively output one of the first and second reference signals as a newly selected reference signal in response to the internal signal , a differential amplification unit configured to amplify the input signal by comparing the input signal with the newly selected reference signal outputted to generate an amplified input signal , and an internal buffer configured to output the internal signal by buffering the amplified input signal .