Abstract: A semiconductor memory chip which has not only a memory array together with address decoding means, but also a self diagnosis means which functions to indicate a defective cell of said memory array has been found. Said self diagnosis means is mounted on the same chip as that of the memory array, and has means for storing information to be stored in the memory array, and means for comparing content of said storing means with output information which is read out of the address at which the information is stored. When the two data do not coincide with each other, an error signal indicating a defective cell in the memory array at the selected address is output.

Abstract: A semiconductor memory chip (FIG. 2) with a memory array (3) is backed-up by a self diagnosis circuit (15, 16, 17, 18, 19) so that an error of a single defective cell, or a single defective row of cells, or a single defective column of cells is automatically corrected. The backup circuit comprises a self diagnosis circuit (15) which has a one-bit memory for storing information in write phase before it is stored in a cell of the memory array (3), and comparison means for comparing the content of said one-bit memory with information immediately read out of the same cell in said write phase, a register means (16, 17) for storing the address of the memory array when said self diagnosis circuit (15) provides an error signal (P) according to the result of the comparison, and an inverter circuit (19) for inverting the output of the addressed memory cell when selected address in read phase coincides with the content of said register means (16,17).