A semiconductor device adjusting an impedance level of an output buffer, includes a replica buffer circuit including a circuit configuration substantially identical to the output buffer, a counter circuit changing an impedance code to vary an impedance level of the replica buffer, a latch circuit temporarily holding the impedance code in response to a control signal, and an end-determining circuit producing the control signal in response to a lapse of a predetermined period from issuance of a calibration command, irrespective of a fact that the replica buffer has not yet reached a desirable impedance level.