The reactive ion etching kinetics of InP studied uses BCl3/Ar and BCl3/Ar/O-2 as etchants. High-temperature etching using BCl3 and Ar increases the etch rate negligibly. However, the addition of 30% oxygen in the gas feed increases etch rates by a factor of 10,000 up to 1.5 micron/min at wafer temperatures of 250 degrees C. X-ray photoelectron spectroscopy analysis reveals that oxygen removes the boron species adsorbing on the InP surface by scavenging the boron to form volatile boron oxides. To study the gas-phase chemistry, optical emission spectroscopy is used to monitor atomic chlorine intensity at different gas mixtures. The chlorine intensity shows a Gaussian-type dependence with oxygen addition, which is similar to the etch rate dependence. Two regimes of etching found are : at temperatures below 150 degrees C, the etching is limited by the removal of indium chlorides; above 180 degrees C, the etching is reaction-limited. The surface morphology shows that the etch profile becomes rougher as a result of increased chemical etching. At high power densities (0.21 W/cm(2)) and intermediate temperatures (150 degrees C), near vertical wall shapes are obtained. A kinetic model for the high-temperature etching is developed as well as a rate law based on the InCl formation reaction. The rate law compares favorably with experimental etch rate results.