US Patent 7466610 Non-volatile semiconductor memory device

A non-volatile semiconductor memory device comprises a redundant memory cell to store address data of a defect cell in a memory cell array. A first decoder circuit is given a first drive voltage to provide a control signal to the redundant memory cell. A dummy memory cell has a threshold voltage corresponding to the redundant memory cell. A second decoder circuit is given a second drive voltage corresponding to the first drive voltage to provide a control signal to the dummy memory cell. A comparator circuit compares data to be read out of the dummy memory cell with data actually read out of the dummy memory cell.