Negative resistance is the phenomenon in which the current through a device decreases as the voltage increases. This is in contrast to conventional logic in which current increases as the voltage increases.While negative resistance exists, there is no such thing as a negative resistor. Negative Resistance exists along some are of the V-I curve in certain electronic components such as the Gunn Diode used in microwave electronics.
In certain regions of the V-I curve, the current drops as the voltage rises.