A low-power high gain-bandwidth monolithic cascode transimpedance amplifier using novel InP/GaAsSb/InP DHBT technology was investigated. The amplifier exhibited state-of-the-art performance of 17.3 dB gain, 12 GHz bandwidth, 55 dBΩ transimpedance, and a corresponding gain-bandwidth of 6.7 THzΩ while consuming only 12.2 mW DC power. It also achieved good gain-bandwidth-product per DC power figure-of-merit (GBP/Pdc) of 7.2 GHz/mW.