Curable silicone composition, sealing material, and optical semiconductor device

Provided is a curable silicone composition capable of forming a cured product having excellent elongation characteristics. The present invention relates to a composition comprising (A) a monovalent hydrocarbon group represented by the average unit formula (I): (R13SiO1/2) a (R12SiO2/2) b (R1SiO3/2) c (SiO4/2) d (XO1/2) e (in the formula (I), R1 is a monovalent hydrocarbon group each independently containing an alkenyl group, where the number of alkenyl groups per molecule is less than 2 on average, X is a hydrogen atom or an alkyl group, 0 < = a < = 1, 0 < = b < = 1, 0 < = clt; 0.9, 0 < = dlt; 0.5, 0 < = ilt; 0.4, a + b + c + d = 1.0, and c + dgt; the problem is solved by a curable silicone composition comprising (A) a resinous alkenyl group-containing organopolysiloxane having an average of less than two alkenyl groups per molecule, (B) an organohydrogenpolysiloxane having two or more hydrogen atom-bonded silicon atoms per molecule, and (C) a curing reaction catalyst. 本发明提供一种固化性有机硅组合物，其能够形成伸长特性优异的固化物。通过包含(A)