This paper studies the effects of gate voltage on heat generation and transport in a metal–semiconductor field effect transistor made of gallium arsenide (GaAs) with a gate length of 0.2 &mgr;m. Based on the interactions between electrons, optical phonons, and acoustic phonons in GaAs, a self‐consistent model consisting of hydrodynamic equations for electrons and phonons is developed. Concurrent study of the electrical and thermal behavior of the device shows that under a source‐to‐drain bias at 3 V and zero gate bias, the maximum electron temperature rise in this device is higher than 1000 K whereas the lattice temperature rise is of the order of 10 K, thereby exhibiting nonequilibrium characteristics. As the gate voltage is decreased from 0 to −2 V the maximum electron temperature increases due to generation of higher electric fields whereas the maximum lattice temperature reduces due to lower power dissipation. The nonequilibrium hot‐electron effect can reduce the drain current by 15% and must be included in the analysis. More importantly, it is found that the electron temperature rise is nearly independent of the thermal package conductance whereas the lattice temperature rise depends strongly on it. In addition, an increase of lattice temperature by 100 K can reduce the drain current by 25%. ©1995 American Institute of Physics.