a p - channel non - volatile memory transistor is programmed by shifting the threshold voltage of the transistor . the threshold voltage is shifted by introducing a programming current to the gate electrode of the transistor , and simultaneously introducing a negative bias to the transistor . the threshold voltage of the p - channel nvm transistor is shifted in response to the negative bias condition and the heat generated by the programming current . the high temperature accelerates the threshold voltage shift . the threshold voltage shift is accompanied by an agglomeration of material in the gate electrode . the agglomeration of material in the gate electrode is an indication of the high temperature reached during programming . the threshold voltage shift of the p - channel nvm transistor is permanent .