A multiple-input NOR logic gate using the negative differential resistance (NDR) circuit is demonstrated. The NDR circuit is composed of four resistors (R) and two SiGe-based heterojunction bipolar transistor (HBT), and it can show the NDR characteristics in the combined current-voltage curve by suitably designing the resistance. Compared to the resonant tunneling diode, the R-HBT-NDR circuit is much easier to be applied to some circuits which are combined with other Si-based or SiGe-based devices and circuits on the same chip. The fabrication is based on the standard 0.35 pm SiGe BiCMOS process. (c) 2007 Elsevier Ltd. All rights reserved.