This letter presents a high power fully integrated single-chip CMOS transmitter for automatic dependent surveillance-broadcast (ADS-B) of unmanned aircraft system (UAS), operating at both 978 MHz Universal Access Transceiver (UAT) mode and 1090 MHz Extended Squitter (1090 ES) mode. The 4.38 mm × 0.95 mm fully-integrated transmitter chip fabricated using 0.18 um CMOS process exhibits modulated output power of 23 dBm at 978 MHz with 102 MHz bandwidth, showing a potential replacement of the state-of-the-art technology by significantly reducing the size and overall cost of the complete ADS-B system. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:432–439, 2017.