A process is provided for producing curable polyorganosiloxanes where noble metal oxides are used as hydrosilylation catalysts. The noble metals can be used in solid granular form or as part of a fixed bed, and do not form part of the final curable composition or cured product. The cured polyorganosiloxanes have increased stability and can be used as encapsulation resins at a temperature far lower than 300° C., have excellent light transmission properties (colorless transparency) in a wavelength region of from ultraviolet light to visible light, light resistance, heat resistance, resistance to moist heat and UV resistance, and do not generate cracks and peeling even in use over a long period of time.