Millimeter-wave integrated circuits (MMICs) are briefly described and system configurations for millimeter-wave passive sensing utilizing MMIC's are reviewed in terms of the type of receiver (tuned RF or superheterodyne) and type of array (focal-plane or aperture). Data on the gain fluctuation which occurs in millimeter-wave field-effect transistors is presented along with an analysis of the effect of this fluctuation on radiometer sensitivity. Two MMIC remedies of this transistor gain fluctuation are then discussed. The first is the stabilization of the gain with a VHF pilot signal path built into a millimeter-wave MMIC low- noise amplifier; this MMIC has been designed, fabricated, and tested and system tests are expected later this year. The second remedy is a MMIC PIN diode switch which can be used as a Dicke load switch at the receiver input. The PIN switch, which also includes a thermal calibration method, can be chopped at a rapid rate (> 1 kHz) relative to the l/F spectrum of the transistor gain fluctuations so that sensitivity is not impaired. The layout and measured performance of a 80 to 100 GHz version of the switch is presented.