Semiconductor memory device having a redundant memory which can be selectively placed in a not-in-use status

A semiconductor memory device, comprising:

• a first memory part, and
• a plurality of redundant circuit means used when said first memory part is faulty;
• each said redundant circuit means comprising
• a second memory part,
• a status memory part means for storing first data indicating whether said memory part is in a not-in-use status or in an in-use status, and for storing said second data indicating an out-of-use status when said second memory part has a failure,
• a faulty address memory part means for storing a faulty address of said first memory part, and
• a comparison circuit means responsive to said status memory part means, for comparing an input address and a memory address from said faulty address memory part when said status memory part is in the in-use status, and outputting a match signal enabling said second memory part to be accessed only when said input address and said memory address from said faulty address memory part both match, and for prohibiting said second memory part from being accessed regardless of a match or a mismatch between the input address and the memory address from said faulty address memory part when said second data stored in said status memory part indicates the out-of-use status.