Aiming at the urgent needs of low 3rd order intermodulation distortion RF amplifiers in wideband large signal capacity wireless systems, this paper presents the optimization design methods of HBT based low 3rd order intermodulation distortion RF amplifiers from two aspects: amplifier bias point optimization and on-chip thermal optimization. The relationship between intermodulation and DC bias condition of Darlington configured RF amplifier was investigated. The DC bias point for optimum 3rd order intercept point (IP3) was obtained. An on-chip heat dissipation optimization circuit structure and a distributed layout were proposed to further improve the IP3. Based on the proposed optimization scheme, a 0.05-1 GHz RF amplifier with low intermodulation was designed in a 2 μm AlGaAs/GaAs HBT process. The tested results show that the amplifier exhibits an output IP3 of 42.1 dBm. The point ratio of IP3-1 dB compression reaches 21.2 dB.