A non-volatile semiconductor memory device includes a plurality of page
buffers, each corresponding to a sense node. Voltages of a first set of
sense nodes are varied according to states of corresponding memory cells
during a first sense period, while voltages of a second set of sense nodes
are fixed at a predetermined voltage. During the second sense period,
voltages of the second set of sense nodes are varied according to states
of corresponding memory cells, while voltages of the first set of sense
nodes are fixed at a predetermined voltage. Using this sensing scheme,
even though a sense node corresponding to an OFF cell is floated, a
voltage of the floated sense node is not coupled down when a voltage of a
neighboring sense node corresponding to an ON cell is lowered.
