A semiconductor memory device with a function of equalizing voltages of dataline pair. After turning off the word line and before turning on the equalization means, the datalines are precharged and discharged to a supplied voltage and ground, respectively. Using the theory of uniform distribution of charges, the datalines are equalized into VCC/2, that is, a half of the source supply voltage. The interference on a weak voltage VCC/2 generator within the equalization means during the equalization mode is thus avoided. The equalization of voltages on the dataline pair can be achieved within a transient cycle. Complete data can thus be written or read before the next command is given.