PURPOSE: An optical semiconductor device is provided to prevent the degradation of a fluorescent substance due to by a heat by separately installing the fluorescent substance from an optical semiconductor. CONSTITUTION: An optical semiconductor is connected to a mounting part(21). The mounting part comprises a cavity(211) which exposes the optical semiconductor in the upper center. An optical device(23) is formed in order to cover the optical semiconductor. The encapsulating material(24) of a light-transmission material is formed within the cavity in order to protect the optical device from outside. The encapsulating material contains one and more fluorescent substances. A depression part is dented on the bottom surface of the cavity. The optical semiconductor is mounted within the depression part.
