Transistor gain is reduced by ioizing radiation, which affects the transistor surface, and by displacement radiation, which causes lattice defects. The investigation of ionizing radiation damage described in this paper was accomplished with X-rays of photon energy less than 150 kev, which is below the energy necessary for displacement damage in silicon. Experiments were performed on silicon dioxide passivated silicon planar transistors with open leads, in a normal amplifying mode and with other junction bias conditions. AC and DC gain measurements at various injection levels showed a gain degradation dependence on the operating bias conditions. Open leads and back-biasing of each junction during irradiation resulted in considerable damage, with almost complete recovery occurring in most transistors tested when the base emitter junction was forward-biased. Many of the characteristics of the radiation damage observed can be explained by Atalla’s model that charge collection at the surface causes a widening of the space charge region, thus increasing the recombination-generation current.