Exposure of GaAs field‐effect transistors to &agr;‐particle radiation has resulted in burnout paths from under the gate to both the source and the drain. Monte Carlo calculations show that the current response from an &agr;‐particle penetrating the center of the gate electrode at normal incidence lasts for 60 ps, about five times longer than predicted by previous hydrodynamic modeling. The thermalization of the induced electrons causes a maximum subsurface heating of the epilayer near the source and the drain when both are held at ground with a negative bias on the gate. A possible melting of the semiconductor will take place at these locations. We present here for the first time a more accurate simulation of the actual lattice heating rates obtained from electron‐phonon exchanges inside the device. Although the qualitative results support the previous hydrodynamic analysis, some important quantitative differences are noted.