A 245 GHz transmitter (TX) with an integrated antenna for sensing applications has been realized, which consists of a push-push VCO with a 1/64 frequency divider, a transformer-coupled one-stage power amplifier, a frequency doubler, and an on-chip antenna with localized backside etching. The frequency of the TX is tunable by an external PLL in the range from 239.5 GHz to 250.8 GHz. The TX is fabricated in 0.13 μm SiGe:C BiCMOS technology with fT/fmax of 300GHz/500GHz. The output power of the TX is 1 dBm at 245 GHz. The TX including the frequency divider dissipates 0.38 W. The EIRP of the transmitter with antenna was measured using an external receive horn antenna. The EIRP reaches about 7 dBm at 245 GHz. This value represents the highest EIRP reported for a 245 GHz transmitter with integrated single antenna so far.