Experiments are reported demonstrating the importance of contact characteristics for the high‐field (average field≳ionization field) microwave emission from InSb. Large voltage drops across the contacts are associated with low threshold currents for the onset of microwave emission. Thermal overloading the contacted sample by high pulse currents results in both a drop in overall resistance and a rise in threshold current and threshold magnetic field. Cessation of microwave emission after a thermal overload may be due to an annealing process in the contact region and is not necessarily connected with any damage to the crystal structure.