A power supply potential GNDP as a substrate potential of two N-channel MOS transistors constructing an SRAM transistor memory cell is enabled to be controlled independent of a ground potential GNDM as a source potential of the N-channel MOS transistors. In the case where a standby current failure occurs, by weakening the driving ability of the N-channel MOS transistors by a substrate effect, the failure can be found in a functional test. A defective memory cell as a cause of the standby current failure, in which a small leak occurs can be specified and is replaced by a redundant memory cell, thereby enabling the yield to be improved.