A new delta‐doped quantum well negative‐differential‐resistance (NDR) switch, grown by molecular beam epitaxy, has been fabricated and demonstrated. A delta‐doped sheet [&dgr;(p+)], located at the center of InGaAs quantum well, provides a potential barrier for electron injection. When a sufficiently high voltage bias is applied, an interesting S‐shaped NDR phenomenon can be observed due to the avalanche multiplication and potential redistribution process. From experimental results, it is known that the environmental temperature plays an important role on the NDR performance. The influence of temperature on the device performance is studied.