Organopolysiloxane, curable silicone composition, cured product thereof, and optical semiconductor

1. A curable silicone composition comprising:

(A) an organopolysiloxane represented by the following average unit formula:

(PhSiO 3/2 ) a (MeViPhSiO 1/2 ) b (Me 2 ViSiO 1/2 ) d .

wherein, “a”, “b”, and “d” are respectively numbers satisfying 0.01≦a≦0.45, 0.01≦b≦0.45, 0.1≦d<0.9, and a+b+d=1;

(B) a straight-chain organopolysiloxane having at least two alkenyl groups and not having any silicon-bonded hydrogen atoms in a molecule, in 0 to 70 mass % of this composition;

(C) an organotrisiloxane represented by the following formula:

HMe 2 SiOPh 2 SiOSiMe 2 H,

in an amount that the amount of silicon-bonded hydrogen atoms in this component is from 0.1 to 5 mol per 1 mol of total alkenyl groups in components (A) and (B); and

(D) an effective amount of a hydrosilylation reaction catalyst.

2. The curable silicone composition according to claim 1 , wherein component (B) is selected from copolymers of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with trimethylsiloxy groups, methylvinylpolysiloxanes capped at both molecular terminals with trimethylsiloxy groups, copolymers of dimethylsiloxane, methylvinylsiloxane, and methylphenylsiloxane capped at both molecular terminals with trimethylsiloxy groups, dimethylpolysiloxanes capped at both molecular terminals with dimethylvinylsiloxy groups, methylvinylpolysiloxanes capped at both molecular terminals with dimethylvinylsiloxy groups, copolymers of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, copolymers of dimethylsiloxane, methylvinylsiloxane, and methylphenylsiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, and combinations thereof.

3. The curable silicone composition according to claim 2 , wherein component (B) is in the composition in a range of 0 to 40 mass % with respect to the composition.