The design of a four-valued multiplexer using the negative differential resistance (NDR) circuit is demonstrated. The NDR circuit used in this work is made of the Si-based metal-oxide-semiconductor field-effect-transistor (MOS) and the SiGe-based heterojunction bipolar transistor (HBT). However we can obtain the NDR characteristic in its combined I-V curve by suitably arranging the MOS parameters. This novel multiplexer is made of MOS-HBT-NDR-based decoders and inverters. The fabrication is based on the standard 0.35 mu m SiGe BiCMOS process. (c) 2008 Elsevier Ltd. All rights reserved.