Chapter 1 begins with basics of quantum mechanics, wave nature of electrons, Schrödinger equation, and extends to the concepts of energy bands and wave vectors. The origins of the semiclassical equation of electron motion are suitably described followed by discussions of confinement effects and tunneling. Chapter 2 introduces semiconductors and fundamentals of carrier transport, Fermi-Dirac distribution and continues to the relevance of generation, diffusion, recombination, and continuity in molecular scale electronics. The chapter concludes with introduction followed by details of p-n junctions and a brief overview of heterojunctions. Chapter 3 entitled MOS Structure and CMOS Devices exposes the readers to metal-oxide-semiconductors (MOS) and associated devices, MOSFET, and CMOS. The structure, operational principles, governing equations for carrier transport as well as the associated circuitry are explained extensively.