This paper presents the effect of different bias circuits configurations on the noise performance of GaAs HBT (heterojunction bipolar transistor) power amplifiers at the receiver band. Various bias circuits have been used for the power amplifier in an WCDMA (wideband code division multiple access) transmitter module including the output duplexer at PCS band (Tx: 1850 ∼ 1910 MHz, Rx: 1930 ∼ 1990. A bias circuit with cascode current mirrors for the 1 st and the 2 nd stages shows less than −180 dBm/Hz receiver band noise with −39 dBc of ACPR (adjacent channel power ratio) at 25.2 dBm antenna output power.