A semiconductor integrated circuit is disclosed. The disclosed semiconductor integrated circuit of the present invention includes a DLL (Delay Locked Loop) controller that controls whether to activate a DLL at the entry of a power down mode, in response to a result of detecting whether a range of phase change of an external clock signal is within a predetermined range, and a DLL block that provides a result of comparing a reference clock signal with a feedback clock signal to the DLL controller and also provides a delay locked clock signal that is periodically updated, in response to the reference clock signal, under the control of an activated output signal from the DLL controller.