Schottky contact properties of films with codeposited CoAl mixture of tri-layered Co/Al/Co structure on GaAs substrate after different rapid thermal annealings (RTAs) have been investigated. Interfacial thermal stability between co-deposited CoAl mixture and GaAs was attributed to the formation of CoAl compound. However, cobalt at the Co/GaAs interface would strongly react with GaAs to produce Co2GaAs phase for tri-layered Co/Al/Co structure on GaAs. Subsequently, Co2GaAs compound would decompose into CoGa and CoAs phases. Capped with a 3500-Å-thick SiO2 layer, co-deposited CoAl films could withstand high-temperature annealing and exhibited a barrier height of 0.88 eV and an ideality factor of 1.08 even after 1050°C rapid thermal annealing for 10 s. As far as the authors are aware, this rapid thermal annealing temperature is the highest in the literature for such excellent Schottky characteristics. The contact was found to achieve a barrier of 0.90 eV for the co-deposited CoAl alloy with Co:Al = 1:1.05 after 850°C rapid thermal annealing for 50 s. Tri-layered Co/Al/Co film was also found to be thermally stable on GaAs after short time annealing (10 s), but the contact property rapidly degraded with annealing time.