Non-volatile memory device and on-chip valley search (OCVS) read method thereof

A non-volatile memory device includes a page buffer and a control logic. The page buffer includes a plurality of latch sets that latches first results of a plurality of first read operations according to a plurality of read signals. The first read operations identify a single page datum from among a plurality of page data of selected memory cells included in a plurality of memory cells. The control logic selects a portion of the read signals by comparing the first results of the first read operations, and resets remaining read signals that are not selected. The page buffer stores second results of second read operations according to the selected read signals, and third results of third read operations according to the reset remaining read signals.