Studies of the etching and vapor polishing behavior of Ge with HI as a function of temperature, linear gas stream velocity, etch rate, and etchant concentration, indicate that temperature is the most significant parameter affecting the smoothness of the etched surfaces. A less pronounced effect is the occurrence of microscopic pitting above a critical etchant concentration. The other parameters did not appear to affect surface characteristics. Less detailed studies of the HI etching of Si have been used to define practical conditions for the vapor polishing of St. A qualitative analysis of the requirements for a usable vapor polish and the experimental conditions necessary to quantitatively define the kinetics of solid-gas etching reactions are presented. © 1965, The Electrochemical Society, Inc. All rights reserved.