A curable composition for semiconductor encapsulation, comprising, as component, a SiH group-containing siloxane compound represented by the following formula; as component, a vinyl group-containing siloxane compound represented by the following formula; as component, a compound having at least three SiH groups or at least three vinyl groups; and as component, a hydrosilylation catalyst: wherein X 1 represents a residue obtainable by excluding hydrogen atoms from the SiH groups of a compound having two SiH groups and having a molecular weight of 1000 or less; X 2 represents a residue obtainable by excluding hydrogen atoms from the SiH groups of a compound having two SiH groups and having a molecular weight of 1000 or less, or a residue obtainable by excluding vinyl groups from a compound having two vinyl groups and having a molecular weight of 1000 or less; Y 1 represents a polysiloxane group represented by the following formula; a represents a number of 0 or 1; and x represents a number from 0 to 10, provided that the compound represented by the formula is such that the mass average molecular weight is 3000 to 1,000,000 as measured by GPC using THF as a solvent and calculated relative to polystyrene standards; the proportion of the number of aryl groups each having 6 to 10 carbon atoms and bonded to silicon atoms, with respect to the sum of the number of alkyl groups each having 1 to 4 carbon atoms and bonded to silicon atoms and the number of aryl groups each having 6 to 10 carbon atoms and bonded to silicon atoms, is 0.05 to 0.5; and the content of Y 1 -CH 2 CH 2 groups is 0.2 mmol/g or less; wherein X 3 represents a residue obtainable by excluding vinyl groups from a compound having two vinyl groups and having a molecular weight of 1000 or less; X 4 represents a residue obtainable by excluding vinyl groups from a compound having two vinyl groups and having a molecular weight of 1000 or less, or a residue obtainable by excluding hydrogen atoms from the SiH groups of a compound having two SiH groups and having a molecular weight of 1000 or less; Y 2 represents a polysiloxane group represented by the following formula; b represents a number of 0 or 1; and y represents a number from 0 to 10, provided that the compound represented by the formula is such that the mass average molecular weight is 3000 to 1,000,000 as measured by GPC using THF as a solvant calculated relative to polystyrene standards; the proportion of the number of aryl groups each having 6 to 10 carbon atoms and bonded to silicon atoms, with respect to the sum of the number of alkyl groups each having 1 to 4 carbon atoms and bonded to silicon atoms and the number of aryl groups each having 6 to 10 carbon atoms and bonded to silicon atoms, is 0.05 to 0.5; and the sum of the contents of Y 2 -CH 2 CH 2 groups and vinyl groups is 0.002 to 0.7 mmol/g or less; wherein R 1 to R 3 each independently represent an alkyl group having 1 to 4 carbon atoms; R 4 to R 6 each independently represent an aryl group having 6 to 10 carbon atoms; R 7 to R 10 each independently represent an alkyl group having 1 to 4 carbon atoms, or an aryl group having 6 to 10 carbon atoms; c, d and e represent numbers that make up the mass average molecular weight of the compound represented by the formula to 3000 to 1,000,000; and wherein R 11 to R 13 each independently represent an alkyl group having 1 to 4 carbon atoms; R 14 to R 16 each independently represent an aryl group having 6 to 10 carbon atoms; R 17 to R 20 each independently represent an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms; f, g and h represent numbers that make up the mass average molecular weight of the compound represented by the formula to 3000 to 1,000,000.