A low-power 1:2 demultiplexer (DEMUX) IC based on a resonant tunneling diode (RTD) is proposed. In order to achieve low-power consumption, the unique negative differential resistance (NDR) characteristics arising from the quantum effect of the RTD are exploited. The proposed DEMUX IC consists of an return to zero (RZ)-mode 1:2 demultiplexing block and an RZ-to-nonreturn to zero converting block, which have a compact structure based on the NDR-based circuit topologies. By implementing the proposed IC using an InP RTD/heterojunction bipolar transistor monolithic microwave integrated circuit technology, 1:2 demultiplexing operation up to 40 Gb/s has been achieved with low-power consumption of 61 mW. In addition, the result is the first demonstration of a 40-Gb/s-level current-mode-logic-type DEMUX IC based on the NDR topology.