Semiconductor memory device and method of operating the same includes an enable signal generator configured to generate first and second enable signals having activation timings determined in response to activation of an active command, the first enable signal being deactivated after a first time from a deactivation timing of the active command, and the second enable signal being deactivated after a second time longer than the first time from the deactivation timing of the active command. Internal voltage generators are configured to generate internal voltages. At least one of the internal voltage generators is turned on/off in response to the first enable signal, and at least one other of the internal voltage generators is turned on/off in response to the second enable signals.