The effects of electromagnetic radiation and high-energy par ticles on semiconductors can be divided into two main processes: (a) the excitation of electrons (the special case is internal ioniza tion, i. e. , the generation of excess charge carriers); and(b) dis turbance of the periodic structure of the crystal, i. e. , the forma tion of "structural radiation defects. " Naturally, investigations of the effects of radiation on semiconductors cannot be considered in isolation. Thus, for example, the problern of "radiation de fects" is part of the generalproblern of crystal lattice defects and the influence of such defects on the processes occurring in semi conductors. The same is true of photoelectric and similar phe nomena where the action of the radiation is only the start of a complex chain of nonequilibrium electronprocesses. Nevertheless, particularly from the point of view of the experimental physicist, the radiation effects discussed in the present book have inter esting features: several types of radiation may produce the same resul t (for example, ionization by photons and by charged particles) or one type of radiation may produce several effects (ionization and radiation -defect formation). The aim of the author was to consider the most typical prob lems. The subjects discussed differ widely from one another in the extent to which they have been investigated.