A method and an apparatus for identifying non-intrinsic defect bits from a population of failing bits for failure analysis to characterize the extrinsic failure mechanisms is provided. Embodiments include performing a failure mode test on a bank of a memory array at different low VDD; determining optimal bank size to observe plateaus of fail counts; determining fail counts of the bank at each different low VDD; determining a plateau of the fail counts; determining whether the plateau represents extrinsic bits of the bank; and submitting the extrinsic bits for root cause analysis.