To provide a curable silicone-based composition having a gas barrier property, causing no warpage of a substrate even when the substrate is subjected to sealing, and providing a transparent cured product having a hardness suitable for dicing.

This curable silicone-based composition includes: (A) a reaction product of an addition reaction between (a) a compound represented by General Formula (1): [where R is an unsubstituted or halogen atom or the like-substituted monovalent hydrocarbon group or alkoxy group] which has in the molecule thereof, two SiH bonds and (b) a polycyclic hydrocarbon having in the molecule thereof, two addition-reactable carbon-carbon double bonds, which has in the molecule thereof, two addition-reactable carbon-carbon double bonds; (B) a linear siloxane containing in the molecule thereof, three or more SiH bonds and a phenyl group; (C) a siloxane compound having an alkoxysilyl group and/or an epoxy group and an SiH bond; and (D) a hydrosilylation reaction catalyst.