Curable silicone composition, cured product thereof, and optical semiconductor device

A curable silicone composition comprising:

• (A) 100 parts by mass of an organopolysiloxane resin having at least two alkenyl groups in a molecule and represented by the average unit formula:
• (R1R22SiO1/2)a(R32SiO2/2)b(R4SiO3/2)c
• wherein R1 is an alkenyl group having from 2 to 12 carbons;
• R2 are 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;
• R3 are 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 such that 0.01≦a≦0.5, 0≦b≦0.7, 0.1≦c<0.9, and a+b+c=1;
• (B) from 5 to 150 parts by mass of an organopolysiloxane represented by the general formula:
• wherein R1 is as defined above;
• R5 are the same or different, and are each an alkyl group having from 1 to 12 carbon atoms or a phenyl group;
• R6 is an alkyl group having from 1 to 12 carbon atoms;
• and m is an integer from 1 to 100, n is an integer from 0 to 50, where m≧n and 1≦m+n≦100;
• (C) is an organosiloxane (C1) represented by the general formula:
• HMe2SiOPh2SiOSiMe2H;
• or
• HMe2SiO(Ph2SiO)2.5SiMe2H;
• wherein Me represents a methyl group and Ph represents a phenyl group;
• or
• (C) is a mixture of the organosiloxane (C1) and an organopolysiloxane (C2) having at least two silicon-bonded hydrogen atoms in a molecule and represented by the average unit formula:
• (HR5R6SiO1/2)d(HR62SiO1/2)e(R52SiO2/2)f(R4SiO3/2)g
• wherein R4, R5, and R6 are as defined above;
• and d, e, f, and g are numbers that satisfy such that 0.01≦d≦0.7, 0≦e≦0.5, 0≦f≦0.7,
• 0.1≦g<0.9, and d+e+f+g=1;
• wherein component (C) is present in the silicone composition in an amount such that the number of silicon-bonded hydrogen atoms in component (C) is from 0.1 to 5 moles per 1 mol of total alkenyl groups in components (A) and (B);
• and
• (D) an effective amount of a hydrosilylation reaction catalyst.