Provided herein are a semiconductor memory device and a method of operating the same. The semiconductor memory device includes a memory cell array including a plurality of memory cells, a status signal generator configured to output an internal status signal indicating whether an operation of the memory cell array has been completed or is being performed and a ready/busy line input mode control unit configured to output a ready/busy signal through a ready/busy line based on the internal status signal or to receive an input signal from an external device through the ready/busy line.