In this paper, three high-gain on-chip antennas are proposed using three different silicon-based technologies in the millimeter-wave/THz frequency range. A modified Vivaldi antenna is first implemented using the micro-fabricated floating process. In the proposed process, the top metal layer is supported by metal vias, separating it from the silicon substrate for low-loss application. The antenna gain of 5.5 dBi is obtained with 78% radiation efficiency. A monopole antenna is subsequently designed using the silicon-benzocyclobutene (Si-BCB) process, with micro-machined backed cavity for high efficiency and wideband application. The simulated gain of this antenna is 6 dBi with 88% radiation efficiency. Our third proposed on-chip antenna is fabricated using commercial 0.18-Hm CMOS technology. The antenna gain and efficiency are improved by the dielectric resonator on the surface of the antenna. The measured gain is 2.7 dBi with radiation efficiency of 43% The three proposed antennas with different silicon compatible processes are therefore suitable for application in the millimeter-wave/THz integrated circuits.