function (φW) by KrF excimer laser irradiation was investigated. From the observed x-ray photoelectron spectroscopy (XPS) results and four-point probe measurements, it is suggested that the surface chemical changes and the laser irradiation time had strong effects on the φW of ITO. Incorporation of oxygen atoms near the ITO surface during laser irradiation induced a peroxidic ITO surface, increasing φW. The induced increase of the ITO φW by laser irradiation could be useful for the enhancement of the hole injection in organic light emitting diodes.