Silicone resin composition for sealing optical semiconductor element and optical semiconductor device

A silicone resin composition for sealing an optical semiconductor element, comprising:

• (A) (A-1) 20 to 100 parts by weight of an organopolysiloxane having a resin structure which contains at least two alkenyl group in one molecule, the alkenyl groups being present at 10 to 70 mol % of total substituent groups bonded to silicon atoms, and
• (A-2) 0 to 80 parts by weight of a linear organopolysiloxane which has an alkenyl group only at both ends of a molecular chain and has a viscosity of 10 to 1,000,000 mPa·s at 25° C. when measured by means of a Brookfield rotary viscometer according to a method described in JIS K 7117-1 provided that a total content of the components (A-1) and (A-2) is 100 parts by weight;
• (B) 3 to 20 parts by weight of an organosiloxane oligomer having at least two alkenyl groups in one molecule and 2 to 5 silicon atoms;
• (C) an organohydrogenpolysiloxane which contains at least one hydrosilyl group and may further contain an alkoxy group or hydroxyl group in one molecule, in an amount corresponding to 0.5 to 4.0 equivalents as a total equivalent of the hydrosilyl groups in the component (C) per unit equivalent of the total alkenyl group in the components (A-1), (A-2) and (B);
• and
• (D) a catalytic amount of an addition reaction catalyst.