Abstract: A semiconductor memory device is subjected to a test operation before delivery from the factory for screening defective products, and can be established in a diagnostic mode for carrying out the test operation when a discriminator acknowledges itself to be expected to produce an internal control signal for the test operation, wherein an instruction signal supplied to the discriminator has active level outside a predetermined voltage range for external signals for a standard access mode of operation so that the semiconductor memory device does not mistakenly enter the diagnostic mode after assembled in an electronic system, thereby preventing the electronic system from malfunction.