A refresh control circuit in a semiconductor memory device includes a refresh controller, a voltage generator and a word line enable circuit. The refresh period controller generates a control signal in response to a self-refresh signal, the control signal indicating a nominal initiation of a refresh period. The voltage generator generates an output voltage in response to the control signal. The output voltage is boosted from a low voltage to a high voltage during the refresh period. The word line enable circuit generates a word line enable signal in response to the control signal, wherein the word line enable signal is activated following a delay after the nominal initiation of the refresh period, and the delay allows the voltage generator to fully boost the output voltage.