A semiconductor memory device includes an internal address generating circuit; an internal command generating circuit; and a memory cell array including one or more memory bank groups. The semiconductor memory device is configured such that when a read command or a write command is input, if a first portion of a plurality of memory banks of a first memory bank group from among one or more memory bank groups of the memory cell array performs a read operation or a write operation, a second portion of the plurality of memory banks of the first memory bank group performs a refresh operation.