The IC presented in this paper is a highly integrated low-power RF transceiver for wireless sensor networks (WSN) compliant with the IEEE 802.15.4 2.4GHz WPAN standard. It contains a radio controller with sleep timer and can perform higher-level MAC functions such as beacon detection and network timing synchronisation autonomously, thereby enabling significant power savings in the overall system. The primary design goal for the receive path is to achieve excellent channel selectivity and dynamic range combined with good sensitivity at very low power consumption, all of which are important parameters for the reliable operation of WSN in the harsh 2.4GHz ISM band. The receiver uses a direct-conversion architecture and offers up to 20dB improved interference rejection in the adjacent channels compared to recently published WPAN transceivers based on the low-IF architecture. Further emphasizing WSN reliability, the receiver supports switched antenna diversity to mitigate multipath fading. Implemented in a 1P6M 0.18mum RFCMOS process, the IC occupies a die area of less than 5.9mmA It operates with a supply voltage from 1.8V to 3.6V, draws 16.8mA in receive mode and 18mA when transmitting at 3dBm.