A 5.5-GHz Doherty amplifier using commercial 0.35-mu m SiGe HBT technology is proposed in this article. To improve the linearity, a predistortion using diode linearizer is adopted for biasing the peak amplifier. Moreover, to realize in fully on-chip with circuit reduction, a 90 degrees 3-dB hybrid coupler and quarter-wave transmission lines are implemented by lumped-elements. In this design, 819 mu m(2) HBTs are used for carried and peak amplifiers, respectively, and 26 mu m(2) HBT is used for linearizer. Results verify that the power gain, P(1dB), and power added efficiency (PAE) of the proposed Doherty amplifier at 5.5 GHz are 8.4 dB, 31 dBm, and 30%, respectively. Also, the adjacent channel power ratio (ACPR) and the output signal's spectrum mask are given using the 54Mcps 64QAM modulated signal at 10 MHz offset. (c) 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1554-1558, 2008.