We have studied the use of optical emission spectroscopy for end point detection in two dry etch applications : SiO2 contact etch in both parallel plate (diode) and high density plasma reactors, and high selectivity poly-Si over SiO2 etch in a chemical downstream reactor, where chemiluminescence is the source of optical emission. We show that useful end point results can be achieved in these processes, using a conventional monochromator/photomultiplier approach, in conjunction with appropriate signal conditioning and end point detection algorithms. Use of a background-correction channel is effective in removing signal drift in the SiO2 contact etch, while use of a large optical aperture is effective in dealing with the very low levels of emitted light in the downstream etch. Important aspects of the signal conditioning and end point detection algorithms are described.