The book focuses on the generalized expression of the Einstein relation composed with the different applied cases. The formulation of Einstein relation involves the countenance of electron concentration, which, in try, is determined by the energy band construction. For numerous semiconductors the electron dispersion relations are dissimilar and therefore all the succeeding formulations become adapted introducing original information. The dispersion relation for bulk materials also variations below magnetic quantization, quantum wells, quantum well wires, in inversion layers and with various types of semiconductor superlattices (SLs). Specially I would like to express my deep gratitude to my beloved Sir Prof. Kamal K. Kar (IIT Kanpur) for various phases of preparing the manuscript. I would like to thank my colleagues and students who have helped me in many stages of preparing the manuscript. I would specifically mention Prof. Samit Kumar Ray (S..N.Bose National Centre for Basic Sciences ), Prof. Pallab Bhattacharya ( University of Michigan) and Prof. Anil K. Bhowmick (IIT Kharagpur) who helped me immensely in numerous ways.