There are several papers 11 to 41 dealing with changes in the properties of GaAs MESFETs upon irradiation with a-particles . In the present note, we concentrated our interest on the changes of the Ids-Uds characteristics of GaAs MESFETs (of a large gate width) taken at small values of Uds (up to 500 mV) and various temperatures from 100 to 294 K after irradiation with 2.84 MeV a-particles at 100 K. The total dose was 4 . 6 ~ 1 0 p~a~rti clesIcm2 for specimen No. 1 and 3 . 8 ~ 1 0pa~rt~icl es/cm2 for specimen No. 2 from a 0.6 mC 241Am source. The GaAs MESFET has a large gate width W = 400 pm, a gate length L 200 pm, and a gate-source or drain-gate spacing about 5 pm. The thickness of the n-type GaAs (concentration 101 7I cm 3 ) active layer is 0.3 pm. In Fig. la and b the experimental results of Ids versus Uds before and after irradiation for two gate biases (0 and -1.0 V) and for two extreme values of temperature (100 and 294 K) are plotted. We observe a significant decrease of Ids after irradiation which is larger at lower than at higher temperatures for both values of U = -1.0 V the change is g larger. The same behaviour is observed after irradiation of GaAs MESFETs with electrons I5 I . (0 and -1.0 V). We notice that for Uds In Fig. 2a and b the results for Ids versus T for three values of U and under a constant Uds = 400 mV are plotted. Before irradiation we observe an increase of Ids as the temperature decreases for both specimens. This is consistent with the temperature dependence of the mobility. At low temperatures the lattice scattering diminishes while the scattering on ionized impurities is predominant. After irradiation we observe the same behaviour for Ids as mentioned above. We must note that the increase of Ids with temperature is small and occurs only for specimen No. 1 (Fig. 2a). For specimen No. 2 (Fig. 2b) we see a very small decrease of Ids with temperature.