In this article we present a low-cost, high-speed, high-accuracy in situ thin film measurement system for real-time process monitoring and industrial process control. This sensor, the two-channel spectroscopic reflectometer (2CSR), is a hybrid of spectroscopic ellipsometry and spectroscopic reflectometry. In 2CSR a polarized beam of white light is directed at the sample, The reflected light is resolved into its two orthogonal components, s and p, using a Wollaston prism. These data, \R-s\(2) and \R-p\(2), are recorded simultaneously as a function of wavelength using a two-channel spectrometer with linear array detectors. The fact that 2CSR has no moving parts, coupled with the use of the two-channel linear array detectors, enables high-accuracy data acquisition across the sensor's spectral range in 6 Ins. This makes the 2CSR ideal for real-time high-speed process monitoring and control in an industrial setting. We have used the 2CSR to make accurate in situ, high speed film thickness measurements during the plasma etching of both silicon dioxide and polycrystalline silicon samples. We show that, in addition to our ability to measure blanket film thicknesses and etch rates, the accuracy of the 2CSR makes this a viable technique for patterned wafer analysis.