To provide a silicone resin composition for sealing an optical semiconductor which has low gas permeability and an optical semiconductor device having high reliability.

The silicone resin composition contains following (A)-(D) components. (A) is expressed by a general formula (1), (in the formula, R¹ is cycloalkyl, R² is a 1-10C univalent hydrocarbon having the same or different substituent or no substituent, x=0.5-0.9, y=0.1-0.5, z=0-0.2, where x+y+x=1.0) and is organosiloxane containing at least two alkenyl in one molecule, (B) is hydrogen organopolysiloxane having two SiH in one molecule, (C) is a catalyst for addition reaction and (D) is an adhesion imparting agent.