This letter presents a 340 GHz cavity-backed on-chip patch antenna design and fabrication using standard 0.13 μm SiGe BiCMOS technology. The patch placed at AM layer is fed by a stripline at LY layer through via holes from LY to AM layer. The via holes are built between the top metal layer (AM layer) and the ground plane (M1 layer) to form a cavity which improves the impedance matching bandwidth and the radiation performances of the antenna. The proposed antenna shows a simulated impedance bandwidth of 9.2 GHz from 335.6 to 344.8 GHz for S11 less than -10 dB. The simulated gain of the antenna at 340 GHz is 3.2 dBi. The total area of the antenna is 0.5×0.56 mm2.