This volume contains the papers presented at the Third International Conference on Neutron Transmutation Doping of Silicon held in Copenhagen on August 27-29, 1980. The first symposium associated with neutron transmutation doping technology as such was arranged in 1976 at Oak Ridge National Laboratory by John Cleland. At this time it had become clear that the technology could be implemented on a commercial scale and that several types of power devices in the electronic industry would benefit from employing neutron transmutation doped silicon in the fabrication proces's'. Two years later the Second International Conference on Neutron Transmutation Doping of Semiconductors was arranged at the University of Missouri, Columbia, by Jon Meese. On this occasion the various aspects of silicon fabrication were reviewed, including irradiation control, radiation induced defects, device optimization, and possible benefits of irradiating other semiconductor compounds. In view of the now wide spread acceptance of neutron doped silicon in the power device industry the present conference was largely directed towards the current status of transmutation doping of silicon. Accordingly, the scope of the three day confe­ rence was to review developments in the technology which had occurred during the two years which had passed since the previous conference. In addition, brief accounts were given with respect to other semiconducting compounds and emerging irradiation techniques which may impact on device design principles in the future.