A method of manufacturing an optical semiconductor device (16) sealed in a transparent or semitransparent cured silicone body (50) by placing an unsealed optical semiconductor device (16) into a mold (23, 34) and subjecting a transparent or semitransparent curable silicone composition (50) that fills the spaces between the mold and the unsealed device (70) to compression molding; provides the sealed optical semiconductor device that is free of voids, allows control of the coating layer thickness, protects the bonding wires from breakage and accidental contact, reduces concentration of stress on an optical semiconductor element, has long service life with reducing discoloration and disconnection of the sealing resin from the optical semiconductor element (16), and has excellent reliability.