This book covers the various material properties of bulk GaAs and related materials, and aspects of the physics of artificial semiconductor microstructures, such as quantum wells and superlattices, made of these materials. A complete set of the material properties are considered in this book. They are structural properties; thermal properties; elastic and lattice vibronic properties; collective effects and some response characteristics; electronic energy-band structure and consequences; optical, elasto-optic, and electro-optic properties; and carrier transport properties. This book attempts to summarize, in graphical and tabular forms, most of the important theoretical and experimental results on these material properties. It contains a large number of references useful for further study. Timely topics are discussed as well. This book will be of interest to graduate students, scientists and engineers working on semiconductors.