A semiconductor memory device and method of operating the same that replaces a fail normal word line that is coupled to a fail memory cell with a redundant word line from a redundant memory block. If the fail normal word line is selected during operation, both the fail normal word line and the redundant word line are activated at the same time to increase capacitance at the sense amplifier. Therefore, it may be possible to increase the exactness of a read operation or a refresh operation, and thereby improve reliability of a device operation by increasing a comparison margin of the sense amplifier.