Sputtered TaSix films on GaAs have been examined as potential refractory Schottky barrier contacts suitable for self-aligned gate fabrication of GaAs MESFETs. The thermal stability of electrical and physical characteristics has been studied following furnace annealing or rapid thermal processing of contacts with compositions near Ta5Si3 (x=06). The electrical characteristics, interface interdiffusion, and evaporation loss of Ga and As through the contact have been examined. The barrier heights of 30-min furnaceannealed contacts were found to increase with temperature over the range 600 to 900°C. The Schottky barrier heights after rapid thermal processing (RTP) of the contacts were fixed at 0.78 eV for temperatures in the range 700 to 900°C. A major finding of this work is that the Schottky barrier contact maintains its integrity even though the equivalent of at least 5 monolayers of Ga and As have decomposed and evaporated through the contact.