Ir/Au Schottky contacts and Ti/Al/Ir/Au ohmic contacts on n-type GaN were investigated as a function of annealing temperature and compared to their more common Ni-based counterparts. The Ir/Au ohmic contacts on n-type GaN with n approximate to 10(17) cm(-3) exhibited barrier heights of 0.55 eV after annealing at 700 degrees C and displayed less intermixing of the contact metals compared to Ni/Au. A minimum specific contact resistance of 1.6 x 10(-6) Omega cm(-2) was obtained for the ohmic contacts on n-type GaN with n approximate to 10(18) cm(-3) after annealing at 900 degrees C. The measurement temperature dependence of contact resistance was similar for both Ti/Al/Ir/Au and Ti/Al/Ni/Au, suggesting the same transport mechanism was present in both types of contacts. The Ir-based ohmic contacts displayed superior thermal aging characteristics at 350 degrees C. Auger electron spectroscopy showed that Ir is superior to Ni as a diffusion barrier at these moderate temperatures. (C) 2007 The Electrochemical Society.