| 摘要 |
PURPOSE: An NOR type mask ROM is provided to improve a sensing margin by reducing leakage current due to a formation of a leakage current path or by preventing the formation of the leakage current path. CONSTITUTION: The NOR type mask ROM includes plurality of first bit lines, plurality of word lines, plurality groups of memory cells, plurality of second bit lines, an array, the first selector(90), the second selector(40), the third selector(50) and the fourth selector(60). The memory cell in the groups are electrically coupled between the adjacent pairs of the first bit lines in parallel. The second bit lines are allocated one by one for each of 4 memory cell groups. The array is divided into plurality of memory cell blocks having 4 of the groups. The first selector(90) electrically couples the second bit lines with corresponding memory cell blocks with response to the first select signal from outside. The second selector selects the second and third groups from the memory cell blocks with response to the second select signal from outside. The third selector selects the first and fourth groups from the memory cell blocks with response to the third select signal from outside. The fourth selector selectively grounds odd number-ed or even number-ed one out of the first bit lines which are commonly used for adjacent memory cell blocks with response to the fourth select signal.
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