A sense amplifier includes a reference signal providing unit and an internal sense amplification unit. The reference signal providing unit provides a reference bit line signal in response to a reference control signal. The internal sense amplification unit receives the reference bit line signal and data signals that correspond to the data. The received signals are provided through bit lines connected to the memory cell array. The internal sense amplification unit senses the received reference bit line signal and the data signals and amplifies the sensed signals. The sense amplifier senses data stored in memory cells connected to dummy bit lines of the outmost memory cell array of a semiconductor memory device such that the memory cells that are not used can be used. Accordingly, the design area and cost of the semiconductor memory device can be reduced.