Abstract: A fully-integrated SiGe BiCMOS Power Amplifier (PA) is presented for the 2.4 GHz 802.11b/g wireless LAN application. The linearization is improved by the simple HBT-capacitor structure in the adaptively biasing circuit, without additional DC power consumption, chip area and insertion loss. The temperature stabilization is achieved in the HBTs DC base biasing path by negative feed back. This scheme prevents effectively thermal runaway and causes no RF power penalty. The proposed power amplifier is fabricated in 0.18 SiGe BiCMOS process and the chip area is 1.56 mm2 including all the biasing and matching circuits. The measurement results indicate that, in band of 2.4-2.5 GHz, this PA gets the small-signal gain S21 of 23 dB, and the input return loss S11of less than -15 dB. The proposed PA achieves the linear output power of 19.6 dBm, the Power Added Efficiency (PAE) of 20%, and the power gain of 22 dB at the output 1 dB compression point.