In this paper, we are presenting two terahertz monolithic integrated circuits (TMICs) for use in next-generation radar and spectroscopy systems operating in the WR-1.5 wavelength band (500 - 750 GHz). Both amplifier circuits have been realized using a 35 nm UnAlAa/InGaAs based metamorphic high electron mobility transistor (mHEMT) technology in combination with a benzocyclobutene (BCB) encapsulation to minimize the device parasitics. Furthermore, airbridge type transmission lines (ABTL) and grounded coplanar circuit topography (GCPW) were applied, leading to a compact chip size and excellent gain performance in the submillimeter-wave frequency regime beyond 500 GHz. A realized six-stage ABTL amplifier circuit demonstrated a small-signal gain of more than 20 dB between 502 and 516 GHz, while a six-stage grounded coplanar TMIC archived a linear gain of 20.3 dB at 610 GHz and more than 18 dB over the bandwidth from 557 to 616 GHz.