A dynamic semiconductor memory device includes a memory cell array including a plurality of memory cells connected between a plurality of word lines and a plurality of bit line pairs. A mode setting portion receives a mode setting code applied from an external portion to generate a power saving mode control signal for a power saving mode of operation responsive to a mode setting command. An address control portion decodes an address applied from an external portion or a refresh address to select one of the plurality of the word lines during a normal mode operation. The address control portion also selects a predetermined number of bits of the address during a power saving mode of operation. The semiconductor memory device, therefore extends the refresh cycle while reducing the refresh time resulting in a lower power consumption.