Importance

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Abstract

Nonvolatile semiconductor storage device provided with first to fourth memory-cell unit each including a first select transistor, a second select transistor series connected to the first select transistor, a third select transistor, and memory-cell transistors series connected between the first and the second select transistors and the third select transistor. The memory-cell transistors have a stack structure including a charge storing layer and a control electrode above the charge storing layer via an insulating film. The first to third select transistors each has a stack structure substantially identical to the aforementioned stack structure. Threshold voltages of the first select transistors in the first and the fourth memory-cell unit and the second transistors in the second and third memory-cell unit differ from the threshold voltages of the second select transistors in the first and the fourth memory-cell unit and the first select transistors in the second and third memory-cell unit.

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First Claim