A data output circuit of a semiconductor memory apparatus includes: a data control driver configured to drive rising data and falling data to output control rising data and control falling data or drive level data to output the control rising data and the control falling data, in response to an output level test signal; a DLL clock control unit configured to drive a rising clock and a falling clock to output a control rising clock and a control falling clock in response to an enable signal and the output level test signal; and a clock synchronization unit configured to synchronize the control rising data and the control falling data with the control rising clock and the control falling clock to output serial rising data and serial falling data.