Growing energy needs of today’s world force the researchers to look for alternative energy sources other than traditional energy forms. Among the alternative energy forms, solar energy seems to be a promising one because it is cheap, clean and unlimited in comparison with the energy needs of the world. In recent years, InSe layered semiconductors of the III-VI family have been a subject of interest both in thin film and single-crystalline form because of certain properties that make it attractive for device applications. In this experimental study, InSe and CdS thin films were deposited by thermal evaporation method onto glass substrates. Schottky and P-N heterojunction devices were fabricated by successive deposition of InSe and CdS thin films onto SnO2 coated glass substrates with various top metal contacts such as Ag, Au, In, Al and C. The structural, electrical and optical properties of the films were investigated prior to characterization of the fabricated devices. The content of this book is based on an experimental study for my Ph.D thesis submitted to Middle East Technical University, Ankara, Turkey in 2004.