A novel bias circuit providing a stable quiescent current for temperature and supply voltage variations is proposed and implemented to a W-CDMA MMIC power amplifier. The power amplifier with the proposed bias circuit has the quiescent current variation of only 6% for the -30 degrees C to 90 degrees C temperature change, and 8.5% for the 2.9 V to 3.1 V supply voltage change, and the variation of the power gain at the 28 dBm output power is less than +/- 0.8 (0.05) dB for the +/- 0.1 V of supply voltage (+/- 60 degrees C of temperature) variation.