Optical research methods make it possible to study the physical properties of semiconductors and, independently of other methods, accurately determine their characteristic parameters. This monograph creatively summarizes the latest results of experimental studies of the optical properties of semiconductors using the example of three groups of materials: elementary semiconductors (Ge, Si), A3V5 compounds (InSb, InAs, GaAs and others), A4V6 compounds (PbS, PbSe, PbTe).