In this paper, general aspects of the reactive ion etching (RIE) technique will be described, such as anisotropy, loading effect, lag effect, RIE chemistries and micro-masking, followed by a brief overview of etching dielectrics (SiOx, SiNx) and crystalline Si. The second section of the paper is dedicated to etching III–V compound semiconductors where, based on RIE results of GaN material, a simple and practical thermodynamic approach is exposed, explaining the criteria for selecting the best chemistry for etching a specific material and explaining the GaN etching results. Finally, a comprehensive study of etching InP-based materials using various chemistries will be discussed, as well as their various photonic applications.