Patent ID: 8120944

Claim:
A nonvolatile semiconductor memory device comprising a memory cell array where memory cells are aligned in a matrix, each memory cell being formed by connecting one terminal of a nonvolatile variable resistive element with two terminals having electrodes at both ends of a variable resistor to one terminal of a selection element with two terminals for controlling a current flowing through the selection element through application of a voltage across the two terminals, or one of two terminals other than a control terminal of a selection element with three terminals for controlling a current flowing between the two terminals through application of a current or a voltage to the control terminal, wherein the memory cells are connected to each other within the memory cell array through first selection lines extending in a direction of rows for connecting the memory cells in a same row, and second selection lines extending in a direction of columns for connecting the memory cells in a same column, a forming process makes the nonvolatile variable resistive element transit between two or more different resistance states when electrical stress is applied across the two terminals of the nonvolatile variable resistive element, so that one resistance state after transition can be used for storing information, a forming detection circuit is provided to detect completion of the forming process on the nonvolatile variable resistive element for each of the memory cells to which a forming voltage for the forming process is to be applied when a plurality of nonvolatile variable resistive elements connected to a same first selection line on which the forming process is to be carried out are selected by applying a current or a voltage to corresponding selection elements through the first selection line, and the forming voltage is simultaneously applied to the selected nonvolatile variable resistive elements through different second selection lines, and the forming detection circuit is configured to prevent the forming voltage from being applied to the second selection lines connected to the nonvolatile variable resistive elements for which the completion of the forming process is detected.