The present invention discloses a method for screening a sensing margin generated by a gate residue in a memory cell transistor. The method for screening failure of the memory cell transistor is summarized as follows. A test mode signal for sensing margin control is supplied. A write operation is performed to store data in the cell transistor. A word line is enabled by an active command. Isolated transistors disposed between a bit line coupled to the cell transistor and a bit line coupled to a sense amplifier are disabled to intercept a sensing operation. A voltage of the bit line coupled to the cell transistor is measured for a predetermined time. Here, voltage variations on the bit line are measured to screen failure of the cell transistor.