A semiconductor memory device is capable of outputting a preset logic level through an EDC pin according to an operation mode during an initial operation, and providing a stable operation according to the specification of the semiconductor memory device just after the input of a data clock (WCK). The semiconductor memory device includes an output circuit configured to output a synchronous data in response to a data clock when the data clock is enabled, and output an asynchronous data when the data clock is disabled, and a data clock detection circuit configured to control outputting the asynchronous data by checking whether the data clock is in a stable state or not.