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