The effect of tin-oxide (SnO) nanoparticles, which are obtained by indium-tin-oxide (ITO) treatment, on the p-GaN surface of GaN-based flip-chip blue micro-light-emitting diode (μ-LED) arrays is investigated. A thin Ag layer is deposited on the ITO-treated p-GaN surface by sputtering. SnO nanoparticles originate from inhomogeneous Schottky barrier heights (SBHs) at Ag/p-GaN contact. Therefore, effective SBH is reduced, which causes carrier transport into the μ-LED to enhance. 10 nm thick ITO-treated μ-LEDs show better optoelectronic characteristics among fabricated μ-LEDs owing to improved ohmic contact and highly reflective p-type reflectors. Basically, SnO nanoparticles help to make good ohmic contact, which results in improved carrier transport into μ-LEDs and thus results in increased optoelectronic performances.