A semiconductor memory device includes a bit line connected to a memory cell; an input/output line configured to input a data signal to the memory cell during a writing operation and to output a data signal stored in the memory cell during a reading operation; and a column select transistor including a first source/drain connected to the bit line and a second source/drain connected to the input/output line, wherein a resistance of the first source/drain is smaller than a resistance of the second source/drain.