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A power amplifier operating at 2.4-GHz is implemented using InGaP/GaAs HBT. The output matching network of the power amplifier is implemented on chip using 2:1 transformer. The transformer has less loss and broad frequency bandwidth in comparison with conventional LC output matching networks. Since a differential power cell is used, the power amplifier gets high gain although a sufficient ballast resistor is introduced. The measured input and output return losses are lower than -10 dB from 2.15 to 3-GHz. The center frequency of the small signal gain is 2.4-GHz, and the 1 dB bandwidth is 0.25-GHz. For 2.4-GHz input signal, power added efficiency at 1 dB compressed output power of 28.3 dBm is 40.2%. The small signal gain is 29.8 dB. We can achieve a power and a gain matching in the same frequency range by using transformer as an output matching network.