A silanol condensation catalyst including at least the zirconium metal salt expressed by Formula (I) below (wherein n is an integer from 1 to 3; each R1 is a hydrocarbon group having from 1 to 16 carbons; and each R2 is a hydrocarbon group having from 1 to 18 carbons.) A heat-curable silicone resin composition for sealing optical semiconductors includes 100 parts by mass of a polysiloxane containing two or more silanol groups in the molecule; from 0.1 to 2,000 parts by mass of a silane compound containing two or more alkoxy groups that are bonded to a silicon atom in the molecule; and a zirconium metal salt expressed by Formula (I). A sealed optical semiconductor is formed by sealing a LED chip by applying the heat-curable silicone resin composition to the LED chip, heating the LED chip, and curing the heat-curable silicone resin composition.