W and WSi ohmic contacts on both p-and n-type GaN have been annealed at temperatures fiom 300 -1000 "C. There is minimal reaction ( S 100 A broadening of the metal/GaN interface) even at 1000 "C. Specific contact resistances in the SZ-cm2 range are obtained for WSi, on Si-implanted GaN with a peak doping concentration of -5 x lo2' ~m -~, after annealing at 950 "C. On p-GaN, leaky Schottky diode behavior is observed for W, WSi, and Ni/Au contacts at room temperature, but true ohmic characteristics are obtained at 250 -300 "C, where the specific contact resistances are typically in the Gcm2 range. The best contacts for W and WSi, are obtained after 700 "C annealing for periods of 30 -120 secs. The formation of P-W2N interfacial phases appear to be important in determining the contact quality.