By monitoring photoluminescence (PL) in real time andinsitu, hydrogen plasma operating conditions have been optimized for surface passivation of native‐oxide‐contaminated GaAs. PL enhancement is critically dependent on exposure time and pressure because of competition between plasma passivation and damage. Optimal exposure time and pressure are inversely related; thus, previous reports of ineffective passivation at room temperature result from overexposure at low pressure. Plasma treatment is effective in removing As to leave a Ga‐rich oxide; removal of excess As increases the photoluminescence yield as the corresponding near‐midgap‐state density is reduced. Passivation is stable for more than a month. These results demonstrate the power of real time monitoring for optimizing plasma processing of optoelectronic materials.