A nonvolatile semiconductor memory of virtual ground array in which a common connection of the sources and a common connection of the drains of nonvolatile memory cells arranged in rows and columns in a memory cell array are used as bit lines, the nonvolatile memory cells including: a reference cell from which a characteristic used as a reference in a differential readout determination operation is obtained; and a neighbor cell at one side of the reference cell, the neighbor cell sharing one of the source and the drain of the reference cell and being connected to a word line which is connected to the reference cell, wherein the nonvolatile semiconductor memory includes a neighbor cell programming circuit to set the neighbor cell to a programmed state when the word line is activated to set the reference cell to a conduction state, the neighbor cell being kept in a non-conduction state during the programmed state.