Light-emitting semiconductor potting composition and light-emitting semiconductor device

A light-emitting semiconductor potting composition comprising

• (A) 100 parts by weight of an organopolysiloxane having a vinyl group at an end of its molecular chain, represented by the average compositional formula (1):
• RaSiO(4−a)/2 (1)
• wherein R is a monovalent organic group, at least 5 mol % of R being phenyl, and “a” is a number of 1.5 to 3.0,
• (B) an organohydrogenpolysiloxane having at least two hydrogen atoms each directly bonded to a silicon atom in a molecule, represented by the average compositional formula (2):
• R1bHcSiO(4−b−c)/2 (2)
• wherein R1 is a monovalent organic group, b is a positive number of 0.7 to 2.1, c is a positive number of 0.001 to 1.0, and the sum of b+c is 0.8 to 3, in an amount to give 0.7 to 10 silicon atom-bonded hydrogen atoms per vinyl group in component (A),
• (C) a platinum group metal catalyst in an amount to give 1 to 1,000 ppm of platinum group metal based on the weight of components (A) and (B) combined, and
• (D) 0 to 10 parts by weight of an organosilicon compound having an alkoxy group bonded to a silicon atom,
• the cured product of said composition having a refractive index of 1.41 to 1.56 at 25° C. and 589 nm (sodium D line).