Since the beginning of semiconductor era in microelectronics the methodology of reliability assessment became a well established area. In most cases the reliability assessment involves statistical methods for safe operating area and long term re- ability parameters at the development of semiconductor processes, components and systems. At the same time in case of catastrophic failures at any development phase the major practical method is failure analysis (FA). However FA is mainly dealing with detection of consequences of some irreversible event that already happened. This book is focused on the most important and the less summarized reliability aspects. Among them: catastrophic failures, impact of local structural inhomo- neities, major principles of physical limitation of safe-operating area (SOA), physical mechanisms of the current instability, filamentation and conductivity modulation in particular device types and architectures. Specifically, the similar principles and regularities are discussed for elect- static discharge (ESD) protection devices, treating them as a particular case of pulsed power devices. Thus both the most intriguing applications and reliability problems in case of the discrete and the integrated components are covered in this book.