In order to improve the Schottky diode characteristics of metal‐In0.52Al0.48As, a new dry photochemical etching and sulfur passivation process has been developed. Excimer and deep UV lamps were used for photochemical etching and surface passivation, respectively. Auger electron spectroscopy measurement shows that this passivation process is as good as wet (NH4)2Sxand P2S5/(NH4)2S passivation in terms of sulfur coverage. Schottky diodes were fabricated onn‐In0.52Al0.48As by electron beam evaporation of a multilayer metal contact of the form Mo/Ti/Pt/Au (2/30/300/200 nm). The leakage current has been reduced by three orders of magnitude after applying this passivation process. X‐ray photoelectron spectroscopy measurements illustrate that these freeS* radicals are capable of replacing As–O and In–O bonds to As–S and In–S bonds. The conclusion is that the As–O and In–O bonds are the primary causes of leakage current. These bonds are dissolved after this photochemical sulfur surface passivation.