A semiconductor device includes data terminal, unit buffers which drive the data terminal and the impedance of which can be adjusted, and control circuits which successively switch the operation of at least two unit buffers selected from unit buffers. Because the operation of the plurality of unit buffers is switched successively, the peak current which flows during an output operation is dispersed, power-supply noise can be controlled, and the output potential can be switched very rapidly and continuously, while a fixed output impedance is maintained.