This paper describes the first fundamental frequency single-chip transceiver operating at -band. The low-IF monostatic transceiver integrates on a single chip two 120-GHz voltage-controlled oscillators (VCOs), a 120-GHz divide-by-64 chain, two in-phase/quadrature (IQ) receivers with phase-calibration circuitry, a variable gain transmit amplifier, an antenna directional coupler, a patch antenna, bias circuitry, a transmit power detector, and a temperature sensor. A quartz antenna resonator with 6-dBi gain and simulated 50% efficiency is placed directly above the on-chip patch to transmit and receive the 120-GHz signals. The circuit with the above-integrated-circuit antenna occupies an area of 2.2 mm 2.6 mm, consumes 900 mW from 1.2- and 1.8-V supplies, and was wire-bonded in an open-lid 7 mm 7 mm quad-flat no-leads package. Some transceiver performance parameters were characterized on the packaged chip, mounted on an evaluation board, while others, such as receiver noise figure and VCO phase noise at the 120-GHz output were measured on circuit breakouts. The AMOS-varactor VCOs have a typical phase noise of at 1-MHz offset and a tuning range of 115.2-123.9 GHz. The receiver gain and the transmitter output power are each adjustable over a range of 15 dB with a maximum transmitter output power of 3.6 dBm. The receiver IQ phase difference, measured at the IF outputs of the packaged transceiver, is adjustable from 70° to 110°, while the amplitude imbalance remains less than 1 dB. The receiver breakout gain and double-sideband noise figure are 10.5-13 and 10.5-11.5 dB, respectively, with an input compression point of . Several experiments were conducted through the air over distances of up to 2.1 m with a focusing lens placed above the packaged chip.