The perception of FTIR spectroscopy as an expensive, non- compact and vibration sensitive analytical technique, is rapidly changing with the recent introduction of small, robust and fast FTIR spectrometers dedicated to in-line and in-situ process control. FTIR Reflectance Spectroscopy has become a powerful in-line characterization technique delivering information on epi-thickness, doping concentration, dielectric film composition, molecular bond density, thickness of thick semiconductor films, deep trenches, etc., inaccessible in the visible range. The metrology capabilities of the technique will be outlined, including a discussion of process integration and semiconductor yield enchantment issues. The new instrument employs a vibrationally isolated FTIR interferometer and a high-speed digitizer. This combination allows a significantly faster scan rate, and a subsequently superior signal-to-noise ratio. The sensor is designed to be mounted on a process chamber equipped with normal or oblique ports, and provides normal or oblique incidence measuring modes. Outstanding vibration suppression, thermal stability, and high S/N makes it possible to achieve process control with monolayer thickness resolution. Particular examples on ULSI thin film/wafer-state FTIR metrology is presented.