A complete 183-GHz CMOS/Indium Phosphide (InP) hybrid heterodyne-spectrometer is realized for spaceborne atmospheric remote sensing applications. It captures spontaneous emission from thermally populated pure rotational states for investigating Earth/planetary atmosphere and interstellar media. Recent missions such as the heterodyne instrument for far-infrared, the microwave limb sounder, and the microwave instrument for Rosetta orbiter highlighted the wealth of scientific knowledge that can be attained by utilizing heterodyne-spectrometers. However, major challenges still remain in mission cost, instrument size, weight, and power (SWaP). Highly integrated CMOS circuits are designed to prototype a low-cost/SWaP spectrometer system and conduct challenging science missions. Within the prototype system, a 183-GHz receiver with a frequency synthesizer is designed in the 28-nm CMOS, and a back-end 6-GS/s 4096-point spectrometer processor is designed in the 65-nm CMOS. The receiver's center frequency is tunable from 180 to 200 GHz. An external InP lownoise amplifier is added at the front-end to provide the required receiver sensitivity. The demonstrated 28-nm CMOS receiver and 65-nm CMOS spectrometer consume 515 mW under 1.5/1.15-V and 1500 mW under 1 V supply, respectively. The complete system achieves 700 to 1000 K noise temperature within the interested bandwidth and RMS uncertainty improvement up to 10 s integration according to the Allan deviation measurements. The spectrometer's capability in detecting gas phase molecular compounds is verified with laboratory trials employing water (H2O) and methyl-cyanide (CH3CN).