A semiconductor memory device and its operating method are disclosed. The semiconductor memory device includes; a memory cell array including a plurality of memory cells selected in relation to a plurality of word lines and a plurality of bit lines, an address decoder selecting at least one word line in response to a refresh address and selecting all of the plurality of bit lines in response to a hidden write signal when a CBR refresh operation is requested during a test mode, a hidden write control circuit generating the hidden write signal when the CBR refresh operation is requested during the test mode, a refresh address generating circuit generating the refresh address when the CBR refresh operation is requested during the test mode, and a data input circuit applying data to all of the plurality of bit lines when the CBR refresh operation is requested during the test mode.