A Cu-metallized InGaP/GaAs heterojunction bipolar transistor (HBT) using a Pd/Ge/Cu n-type ohmic contact, a Pt/Ti/Pt/Cu p-type ohmic contact, and a Ti/Pt/Cu interconnect has been fabricated for power applications. The 4 × 20 μm2 HBT had an output power of 11.25 dBm with a power-added efficiency of 35.1%. After applying current-accelerated stress for 24h, the current gain remained larger than 125. The device was also annealed at 200°C for 24 h, and showed a slight decrease in output power from 10.06 to 9.83 dBm. The results demonstrated that reliable Cu metallization can be used for fabricating InGaP/GaAs HBTs for power applications.