The forward current of Pd/GaN and Pt/GaN Schottky diodes is found to increase significantly upon introduction of H2 into a N2 ambient. Analysis of the current–voltage characteristics as a function of temperature showed that the current increase is due to a decrease in effective barrier height through a decrease in metal work function upon absorption of hydrogen. The introduction of 10% H2 into a N2 ambient was found to lower the effective barrier height of Pd on GaN by 50∼70 meV over the temperature range of 298 to ∼423 K and of Pt on GaN by 30∼60 meV over the range of 443 to ∼473 K. The magnitude of the changes increased with temperature due to the effective cracking of the H2. The changes in barrier height were completely reversible upon restoration of N2 ambient.