Abstract The experimental study of the radiation damage on the electrical properties of silicon planar transistors is described. An attempt is made to have a general view to the problem and specially to give valuable informations about the optimum conditions of the choice and the utilisation of the device to the circuit designer. We have used a wide variety of radiation sources in order to check the validity of the equivalence between particles and energies. The degradation rate of dc and ac gain has been studied as a function of the injection level and the bias conditions under radiation. We also described the behaviour at very low currents, the variations in high frequency and commutation parameters, the thermal recovery and the dose rate influence.