Semiconductor memory device having plural memory mats with centrally located reserve bit or word lines

摘要

A semiconductor memory device having reserve bit lines or word lines for replacing defective bit lines or word lines which can increase a defect relief probability and improve an operational margin. The reserve bit lines or word lines are provided approximately in a central portion of a memory mat. Because of a low probability of defect occurrence in the reserve word lines or bit lines, the probability of defect occurrence can be made low when a defective word line or bit line is replaced with a reserve word line or bit line.