Abstract: Thermally stable ohmic contacts of Au/Ti/W/Ti on n-GaAs were fabricated using magnetic spattering unit and rapid thermal annealing. The electrical and structural properties of Au/Ti/W/Ti ohmic contacts were studied by measuring the contact resistivity and analyzing Auger Energy Spectrum （AES） and X-ray Diffraction （XRD） spectrum. Electrical measurement shows a minimum ohmic contact resistivity of 1.5×10^-4Ωcm² at 700℃. It is found that a TiAs phase in the interface between metal multilayer and n-GaAs is responsible for the ohmic contact performance.