US Patent 7529130 Semiconductor memory device

A semiconductor memory device includes: a memory cell array with electrically rewritable and non-volatile memory cells arranged therein; and a sense amplifier circuit configured to read out data of the memory cell array, wherein a plurality of information cells, in each of which one of M(M≧2) physical quantity levels is written, and at least one reference cell, in which a reference physical quantity level is written, are defined in the memory cell array, and the sense amplifier circuit detects a cell current difference between the information cell and the reference cell selected simultaneously in the memory cell array to sense data defined by the M physical quantity levels of the information cell.