To provide a phenolic hydroxy group-bearing compound as a component of a thermosetting resin composition giving a cured product having heat resistance and low elasticity at high temperatures, to provide such a thermosetting resin composition, and to provide a semiconductor sealing material.

The compound is such as to have in the molecule one addition-reacted part that is formed by Diels-Alder reaction from (a) a phenolic hydroxy group-bearing conjugated diene structure and (b) a phenolic hydroxy group-bearing dienophilic structure, wherein the addition-reacted part is such that at least one phenolic hydroxy group on each of both the structures constituted of the structures (a) and (b) respectively, wherein the Diels-Alder addition-reacted part has the phenolic hydroxy groups that dissociate at 200°C or higher.