Gallium arsenide Schottky barrier junctions have become increasingly important in a wide variety of high performance GaAs microwave devices such as IMPATT diodes, Schottky gate FETs and RF detectors. Although neutron irradiation effects on silicon Schottky barrier junctions are well documented no detailed results have been reported for GaAs Schottky junctions. The purpose of this program was to explore the effect of fast neutron irradiation on the metal semiconductor interface and the resultant performance of Schottky barrier (including with transient ionizing radiation). Device changes at neutron fluences where the reduction in free carrier concentration is less than 20% were emphasized, as larger reductions in free carrier concentration l lead to gross changes in junction properties that cannot be tolerated in most applications. Gold and aluminum were selected as the metals for forming the Schottky junctions since there is a large variety of results for Au-GaAs Schottky junctions reported in the literature, which could be used for comparison purposes, and because the Al-GaAs junction has a lower barrier height and appears to be more stable than the Au-GaAs interface.