CMOS (Complementary Metal Oxide Semiconductor) transmitter and receiver circuits for rotational spectroscopy are demonstrated. The IC's implemented in 65-nm CMOS consist of a 208-252 GHz transmitter and a 225-280 GHz receiver. Use of CMOS electronics can reduce the cost of electronics for rotational spectrometer application from over $50k to less than $1k. The receiver (RX) includes an on-chip antenna for air-to-chip interface, a 2nd order sub-harmonic down-conversion mixer, a low noise IF amplifier and an amplitude detector. The transmitter (TX) includes an on-chip antenna for chip-to-air interface, Fractional-N synthesizer with a frequency step less than 1 kHz with a built-in frequency shift keying circuit as well as a frequency up-converter to generate the signal at the RF. The integrated circuits were assembled into a rotational spectrometer and utilized to detect numerous gases including Ethanol and Acetone in human breath. It is the first ever demonstration of spectroscopy on pure gases as well as breath using CMOS circuits, and this work paves the way toward a more compact, affordable and efficient rotational spectroscopy system.