A semiconductor system may include a controller configured to provide a first external clock and a control signal to a semiconductor device, and the semiconductor device configured to transmit/receive external data and a plurality of second external clocks to/from the controller, wherein the plurality of second external clocks comprise a third primary external clock and a third secondary external clock, and the semiconductor device transmits both of the third primary external clock and the third secondary external clock to the controller or to transmits one of the third primary external clock and the third secondary external clock to the controller, based on an operation select signal.