This paper describes an ultra-low-power RF transceiver implemented as part of a system-on-chip. The transceiver operates in the 868/915 MHz frequency band using binary FSK modulation at a 45 kbit/s data rate. It achieves -89 dBm receiver sensitivity and -6 dBm transmitter output power while consuming 1.6 mA and 1.8 mA, respectively, from a 1.2 to 1.5 V supply. It is fabricated in 0.13 mum CMOS occupying 1.5 mm2, and it uses only four external components (i.e., battery, antenna, SAW-filter and crystal). The transceiver offers a small form factor, low cost and low power solution for wireless sensor network applications.