NOVELTY - A curable composition comprises an addition reaction product (A) of aryl group-containing compound (a) (I) containing hydrogen atoms bonded with silicon atoms in a molecule, polynuclear hydrocarbon (b) containing addition reaction carbon-carbon double bond in a molecule, and silicon-containing compound (c) (II) containing hydrogen atoms bonded with silicon atoms in a molecule, compound (B) containing 3 or more addition reaction carbon-carbon double bonds in a molecule, and hydrosilylation catalyst (C) containing platinum group metal.    USE - Curable composition is used for forming semiconductor device (claimed) e.g. light-emitting diode, semiconductor laser, photodiode, phototransistor, and solar cell. Can also be used as lens material, sealing material for optical device and electronic device, insulating material, and coating material.    ADVANTAGE - The curable composition has excellent flexibility, gas-barrier property, crack resistance, and protection property of silver electrode with respect to corrosive gas, and high expansion ratio and strength, and provides cured material with excellent light transmittance and transparency.    DETAILED DESCRIPTION - A curable composition comprises an addition reaction product (A) of aryl group-containing compound (a) of formula (I) containing hydrogen atoms bonded with silicon atoms in a molecule, polynuclear hydrocarbon (b) containing addition reaction carbon-carbon double bond in a molecule, and silicon-containing compound (c) of formula (II) containing hydrogen atoms bonded with silicon atoms in a molecule, compound (B) containing 3 or more addition reaction carbon-carbon double bonds in a molecule, and hydrosilylation catalyst (C) containing platinum group metal.    R1=1-12C monovalent hydrocarbyl optionally substituted by halo, cyano, glycidoxy, or 1-6C alkoxy;    R2=optionally substituted monovalent hydrocarbon group other than addition reaction carbon-carbon double bond, or alkoxy;and    n=1-4.    An INDEPENDENT CLAIM is included for semiconductor device.