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