Characteristics of diodes and transistors by X-ray irradiation have been studied. The X-rays were obtaind by the 2MV Van de Graaff accelerator of Kyoto University using the brems-strahlung of 1.5MeV electrons upon gold target. The reverse current of 1S120 diodes increased gradually up to about 1X104 (rad (Si)) and steeply or rather steeply above this dose. The 70% recovery time was about 110 hours. The gain of 2SC183 transistors operated actively at constant emitter current, generally degraded more according to larger collector-base current. The radiation damage of 2SC476 transistors was found greater than that of 2SC183, both under passive operation. These facts would be attributed to the surface effect, that is, an increase of recombination velocity on the semiconductor surface.