A semiconductor memory device includes a delay lock loop (DLL) performing a locking operation at a wide frequency range and reducing current consumption. The semiconductor memory device includes a (DLL) having serially connected delay cells that receive and delay an external clock signal, wherein a predetermined number of delay cells of the serially connected delay cells that are to perform a delay operation are turned on in response to a threshold frequency recognition signal and first and second delay cell on signals, and for generating an internal clock signal; and a controller for generating the threshold frequency recognition signal and the first and second delay cell on signals, which reduce current consumption of each of the serially connected delay cells and increase a period of delay time thereof, if more delay cells are to be turned on when a delay cell indicating a threshold frequency is turned on.