The book contains thorough and complete analytical calculation of transverse wavevector dependent transmission coefficient of the semiconductor nanostructure called single rectangular tunnel barrier. Thorough numerical investigations are presented to bring out dependence of transmission coefficient on angle of incidence, transverse wavevector, total energy and longitudinal part of total energy of incident electron. Complete explanations are presented of results of numerical investigations. Physics of the problem has been solved completely in this book. Interested reader will be able to enjoy the Physics with complete satisfaction. The book is self-contained; it contains background on Nanostructure Physics, Microelectronics and Quantum Mechanics to enable the reader assimilate the book completely.