A 320 GHz fully integrated terahertz imaging system is reported. The system is composed of a phase-locked high-power transmitter and a coherent high-sensitivity subharmonic-mixing receiver, which are fabricated using a 130 nm SiGe BiCMOS technology (f_T/f_max = 220/280 GHz). To enhance the imaging sensitivity, a heterodyne coherent detection scheme is utilized. To obtain frequency coherency, fully integrated phase-locked loops are implemented on both the transmitter and receiver chips. According to the measurement results, consuming a total dc power of 605 mW, the transmitter chip achieves a peak radiated power of 2 mW and a peak EIRP of 21.1 dBm. The receiver chip achieves an equivalent incoherent responsivity of more than 7.26 MV/Wand a sensitivity of 70.1 pW under an integration bandwidth of 1 kHz, with a total dc power consumption of 117 mW. The achieved sensitivity with this proposed coherent imaging transceiver is around ten times better compared with other state-of-the-art incoherent imagers. To the best of our knowledge, this paper demonstrates the first fully integrated coherent terahertz imaging transceiver on silicon.