A semiconductor device includes an output circuit having a plurality of unit buffer circuits, an impedance of each unit buffer circuit of the plurality of unit buffer circuits being adjustable, a control circuit configured to selectively activate one or more unit buffer circuits of the plurality of unit buffer circuits, and an impedance adjustment unit configured to adjust the impedance of each of the unit buffer circuits of the plurality of unit buffer circuits. The impedance adjustment unit includes a first power line, a replica circuit, and a load current generation circuit. The replica circuit and the load current generation circuit are coupled in common to the first power line, the replica circuit has a replica impedance that is substantially equal to the impedance of the output circuit, and the load current generation circuit changes current flowing therethrough.