Curable silicone composition, cured product thereof, and optical semiconductor

A curable silicone composition comprising:

• (A) an organopolysiloxane having at least two alkenyl groups in a molecule and represented by the following average unit formula:
• (R1R22SiO1/2)a(R32SiO2/2)b(R4SiO3/2)c
• wherein, R1 is an alkenyl group having from 2 to 12 carbons;
• each R2 is the same or different, and are each an alkyl group having from 1 to 12 carbons, an alkenyl group having from 2 to 12 carbons, an aryl group having from 6 to 20 carbons, or an aralkyl group having from 7 to 20 carbons;
• each R3 is the same or different, and are each an alkyl group having from 1 to 12 carbons, an alkenyl group having from 2 to 12 carbons, or a phenyl group;
• R4 is an aryl group having from 6 to 20 carbons or an aralkyl group having from 7 to 20 carbons;
• and a, b, and c are numbers that satisfy the following conditions:
• 0.01≦a≦0.5, 0≦b≦0.7, 0.1≦c<0.9, and a+b+c=1;
• (B) a straight chain organopolysiloxane having at least two alkenyl groups in a molecule and having no silicon-bonded hydrogen atoms, in an amount of 0 to 70% by mass of this composition;
• (C) an organosiloxane (C1) represented by the following general formula:
• HR5R6SiO(R72SiO)nSiR5R6H
• wherein, each R5 is the same or different, and are each an alkyl group having from 1 to 12 carbons;
• each R6 is the same or different, and are each an aryl group having from 6 to 20 carbons or an aralkyl group having from 7 to 20 carbons;
• each R7 is the same or different, and are each an alkyl group having from 1 to 12 carbons or a phenyl group;
• and n is a number from 0 to 100,
• an organopolysiloxane (C2) having at least two silicon-bonded hydrogen atoms in a molecule and represented by the following average unit formula:
• (HR5R6SiO1/2)d(HR52SiO1/2)e(R72SiO2/2)f(R6SiO3/2)g
• wherein, R5, R6, and R7 are as defined above;
• and d, e, f, and g are numbers that satisfy the following conditions:
• 0.01≦d≦0.7, 0≦e≦0.5, 0≦f≦0.7, 0.1≦g<0.9, and d+e+f+g=1, or
• a mixture of components (C1) and (C2), in an amount such that the number of silicon-bonded hydrogen atoms in this component is from 0.1 to 5 moles per 1 mol of total alkenyl groups in components (A) and (B);
• and
• (D) an effective quantity of a hydrosilylation reaction catalyst.