The Rh/n-GaAs contacts with and without sulfur passivation were examined. It was demonstrated that passivation results in contacts of better quality and improved thermal stability. The passivated contacts had higher barrier height, lower reverse current, and lower ideality factor. The formation of thermally stable S-S, S-Ga, and S-As bonds at the GaAs surface, suppression of thermally generated defects, and possible modification in the charge and structure of native oxide were used to explain the observations.