This paper presents a single-chip CMOS transmitter for Automatic Dependent Surveillance-Broadcast (ADS-B) system, for the first time, operating at both 978 MHz Universal Access Transceiver (UAT) mode and 1090 MHz Extended Squitter (1090 ES) mode. The 1.9 mm × 0.84 mm transmitter chip fabricated using 0.18 um CMOS process exhibits peak output power of 17 dBm at 978 MHz with 128 MHz bandwidth, thus providing a big advantage of reduction in size and cost over the state-of-the-art ADS-B technology.