Dynamic random access memory device having first and second I/O line groups isolated from each other

A dynamic random access memory device has a memory cell array which includes a first memory cell array part and a second memory cell array part portioned in a first direction parallel with the bit lines, a plurality of column switches, one provided for each of the bit lines, a plurality of input/output lines each connected to different ones of the bit lines via associated ones of the column switches, a row address decoder for decoding a first portion of an address signal and a column address decoder for decoding a second portion of the address signal to thereby simultaneously access at least two memory cells with the address signal. The input/output lines extend in a second direction parallel with word lines and are divided into first and second groups of input/output lines connected to those bit lines which belong to the first and second memory cell array parts, respectively in which the first input/output line group is isolated from the second input/output line group. A first input/output gate circuit is connected to the first group of input/output lines and a second input/output gate circuit is connected to the second group of input/output lines, in which the first and second input/output gate circuits serve to selectively transfer therethrough, between main amplifiers and the first input/output line groups, data to be simultaneously read from or written into the at least two memory cells in the memory cell array.