A semiconductor memory device comprises a memory cell configured to output data to a pair of bitlines, a variable delay circuit configured to receive a sense amplifier enable signal, adjust a delay of the sense amplifier enable signal by changing a slope of a delay based on a variable external power supply voltage, and output a delayed sense amplifier enable signal, and a bitline sense amplifier configured to amplify a voltage difference between the pair of bitlines in response to the delayed sense amplifier enable signal and output the amplified voltage difference to a pair of input/output lines.