High‐field effects in metal‐oxide‐semiconductor capacitors have been studied in detail. A comprehensive set of experiments, stressing identically fabricated capacitors on bothP‐type andN‐type silicon, both in accumulation and in inversion, has been made to study defect generation in the oxide at high fields. There is clear experimental evidence that both bulk hole and electron traps are generated under all stress conditions. High‐field prebreakdown properties depend mainly upon the dynamics of generation of traps, trapping and detrapping at these and in previously existing traps. It has been found that of several processes, some dominate, depending upon the type of silicon and polarity during stressing, and this is also true for the final breakdown mechanism. In this paper the dominant mechanisms are identified for each of the field stress conditions that have been studied.