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A new on-chip linearizer self-adapting to the input power has been devised and implemented on a highly linear monolithic microwave integrated circuit (MMIC) power amplifier for 1.95 GHz wide-band code division multiple-access (W-CDMA) systems. The linearizer consists of an InGaP/GaAs heterojunction bipolar transistor (HBT) active bias circuit and reverse biased junction diode for which the dynamic admittance to input power level varies adaptively to control RF transmission power to the bias circuit. The proposed linearizer effectively improves the gain compression with little insertion power loss, and more importantly, it consumes no additional die area and DC power. The HBT MMIC power amplifier with the integrated linearizer exhibits a maximum output power of 30.3 dBm, a power gain of 27.5 dB, a power added efficiency of 42% at the maximum output power under an operation voltage of 3.4 V, and adjacent channel leakage power ratio of -38 dBc at 27 dBm of output power.