| 摘要 |
A semiconductor memory comprises a reading circuit including a memory cell composed of a selection transistor and a memory transistor having a floating gate, a reading reference circuit having a dummy memory cell having the same construction as that of the memory cell, and a comparator for receiving and comparing an output of the memory cell of the reading circuit and an output of the dummy memory cell of the reading reference circuit. A voltage supply circuit applies a predetermined voltage to a control gate of a dummy memory transistor of the dummy memory cell so as to cause a drain current to flow through the dummy memory transistor. The output of the memory cell in a written condition is compared with the output of the dummy memory cell, and when the output of the memory cell in a written condition is consistent with the output of the dummy memory cell, a threshold voltage of the memory transistor in the written condition is estimated on the basis of the predetermined voltage applied to the control gate of the dummy memory transistor.
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