A curable organopolysiloxane composition comprising (A) a linear organopolysiloxane having at least two alkenyl groups and at least one aryl group per molecule, (B) a branched organopolysiloxane having at least one alkenyl group and at least one aryl group per molecule, and having siloxane units represented by the general formula: RsiO2/3, (C) a linear organopolysiloxane with both terminal ends of the molecular chain blocked by silicon bonded hydrogen atoms having at least one aryl group per molecule, and (D) a hydrosilation reaction catalyst, and a semiconductor device whose semiconductor elements are coated with the cured product of the above-described composition. The curable organopolysiloxane composition shows low viscosity, excellent filling properties, and excellent curability that cures to form a soft cured product of a large refractive index, high light transmittance, and high adhesion to substrates, as well as the semiconductor device shows superior reliability.