The secondary ion mass spectrometry, X-ray diffraction, electron probe and scanning electron microscope were employed to analyze qualitatively the metallurgical and corresponding electrical properties of the interfaces between Pt, Mo, Ti, Al and GaAs, which have been subjected to heat treatment at various temperatures. The results are discussed. Based on these results, we are able to suggest the physical characteristics that the metal should possess and the principle for preparing the junction that should be employed in order to obtain a good Schottky junction on GaAs.