US Patent 7573772 Semiconductor memory device and self-refresh method therefor

A semiconductor memory device and a self-refresh method in which the semiconductor memory device includes a plurality of input/output ports having respective independent operation, a period of self-refresh through one of the plurality of input/output ports being subordinate to a kind of operation through another input/output port. Whereby, a refresh characteristic in a multi-port semiconductor memory device including a dual-port semiconductor memory device may be improved.