A clock receiver in a semiconductor integrated circuit includes a first clock buffer configured to buffer an external clock to generate a low frequency buffered clock in response to a first operation signal; a second clock buffer configured to buffer the external clock to generate a high frequency buffered clock in response to a second operation signal; and an internal clock generating unit configured to receive the low frequency buffered clock and the high frequency buffered clock, to control states of the first operation signal and the second operation signal and to generate an internal clock.