This link seems to explain it in some detail: https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance https://en.wikibooks.org/wiki/Circuit_

This link seems to explain it in some detail: https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differen... A typical transistor doesn't have the red part of the curve where resistance goes up with increased current. This effect might be useful for multi-level logic or for self current limiting (similar to a lamp)?