The negative resistance phenomenon of metal-insulator-metal diode is investigated experiment-ally with an Al-Al2O3-Au thin film composite. This residual effect, which is characteristic of the negative diode, is shown to be caused by a particular state of conduction, subjected to temperature and applied voltage. The “voltage memory effect” is also shown on the voltage-current curve of the negative diode. Between 0.1_??_3.0c/s of frequency, the negative resistance is dispersive, and beyond 3.0c/s, the diode shows no longer the negative resistance. The exact mechanism of the negative resistance remains still unexplored.