Abstract: Curable silicone compositions, encapsulants including the same, and optical semiconductor devices including the encapsulants are provided herein. In an embodiment, a curable silicone composition includes: (A) an alkenyl group-containing organopolysiloxane having at least two alkenyl groups per molecule; (B) an organohydrogenpolysiloxane having at least two silicon atom-bonded hydrogen atoms per molecule; (C) an epoxy group-containing resinous organopolysiloxane represented by Average Unit Formula (I): (R13SiO1/2)f(R22SiO2/2)g(R1SiO3/2)h(SiO4/2)i(XO1/2)j wherein R1 are independently halogen-substituted or unsubstituted monovalent hydrocarbon groups, at least two R1 are alkenyl groups; R2 are independently halogen-substituted or unsubstituted monovalent hydrocarbon groups or epoxy group-containing organic groups, wherein at least one R2 is an epoxy group-containing organic group; X is a hydrogen atom or an alkyl group; 0?f<1; 0<g<1; 0?h<0.9; 0?i<0.5; and 0<j<0.5; f+g+h+i+j=1.

Abstract: A curable silicone composition is capable of forming a cured product having excellent elongation characteristics. The curable silicone composition, comprises: (A) a resinous alkenyl group-containing organopolysiloxane containing less than two alkenyl groups per molecule on average, which is represented by average unit formula (I): (R13SiO1/2)a(R12SiO2/2)b(R1SiO3/2)c(SiO4/2)d(XO1/2)e, where in formula (I), each R1 is independently a monovalent hydrocarbon group including an alkenyl group, while the number of alkenyl groups per molecule is less than two on average, X is a hydrogen atom or an alkyl group, 0?a?1, 0?b?1, 0?c?0.9, 0?d<0.5, 0?e<0.4, a+b+c+d=1.0, and c+d>0; (B) an organohydrogenpolysiloxane having two or more silicon atom-bonded hydrogen atoms per molecule; and (C) a curing reaction catalyst.

Abstract: A curable silicone composition comprises (A) a resinous alkenyl group-containing organopolysiloxane including at least two alkenyl groups per molecule and at least one (SiO4/2) unit, (B) a resinous organohydrogenpolysiloxane including at least two silicon atom-bonded hydrogen atoms per molecule and at least one (SiO4/2) unit, (C) a catalyst for hydrosilylation reaction, and (D) a curing reaction inhibitor. The curable silicone composition exhibits practically effective curability even at low temperatures, has a low shape deformation and shrinkage rate during curing, can be cured in a short period of time, and can form a transparent and high-hardness cured product.