Abstract: An addition-curable silicone composition includes organopolysiloxane having at least two alkenyl groups bonded to a silicon atom per molecule; an organosilicon compound having at least two silicon atom-bonded hydrogen atoms per molecule; a platinum group metal-based catalyst; and an inorganic oxide particle. The inorganic oxide particle is surface-treated by a polysilazane compound-containing composition that includes an organic solvent and a polysilazane compound in which a ratio of a number of repeating units represented by the following formula (2) is 0 to 0.5 relative to a total number of repeating units represented by the following formulae (1) and (2) wherein in the formulae, R represents a group selected from the group consisting of an aliphatic hydrocarbon group, an aromatic hydrocarbon group, and an alkoxy group.