The thermal stability of Ti/Pt/Au Schottky contacts on n-GaAs with Ti films 0-60 nm is investigated. The contacts with Ti films as small as 10 nm remain thermally stable with annealing up to 400 degrees C. The changes induced by thermal treatment in the electrical characteristics of the contacts are correlated with the Rutherford backscattering and microscopic analysis of the annealed samples. It shows profuse interdiffusion and interfacial reaction with 300 degrees C anneal for the GaAs/Pt/Au system. It has been found that introducing the Ti film between GaAs and Pt/Au, the interdiffusion of Pt and Au is also prevented. These results are useful for reducing the gate metallisation resistance of metal semiconductor field effect transistors.