A variety of reflectance techniques have been developed to determine the thickness of thin transparent films on silicon substrates 1,2 These techniques are based on the way incident radiation is reflected from air-film and film-substrate interfaces. These reflectance techniques are ideally suited to measuring films ranging in thickness from approximately 500 A to many thousands of angstroms. The absolute reflectivity technique measures the reflectance at several wavelengths and, by matching the curve as measured to the theoretical, the actual film thickness can be determined. A refined version of the absolute reflectivity technique is the Brewster's angle spectrophotometer. This article describes the development phase for an automatic Brewster's angle spectrophotometer and discusses the performance of the instrument. The optical and mechanical layouts and photographs depict the choice of implementation.