US Patent 7652943 Semiconductor memory device, test circuit and test method

Disclosed is a semiconductor memory device having memory cells that are in need of refresh for data retention, includes control circuits for necessarily generating the refresh immediately before the read/write operation, and for setting the latency to a first fixed value at all times, for the first mode during the testing, and for necessarily generating the refresh immediately after the read/write operation, and for setting the latency to a second fixed value at all times, for the second mode during the testing.