Nuclear irradiation of pnp junctions shows a pronounced change on their output electrical characteristics. Theoretical analysis, using computer programming (TRANSRAD), shows that exposing silicon transistors to nuclear radiation (neutrons, protons, electrons and gamma-rays) causes the devices to lose most of their forward gain factor. For all the analyzed irradiation conditions both junction leakage current and breakdown voltage are shown to increase pronouncely. The damage effect is found to be function of radiation fluence and energy.