To achieve an excellent high-temp. resistance by forming a curable compsn. contg. a hydrogenated silicone copolymer and a hydrosilylation catalyst.

A cyclic organosiloxane (e.g. octamethylcyclotetrasiloxane) is thermally reacted in the presence of an alkali metal silanolate catalyst. The resultant hydrogenation product [e.g. HOSiR1R2(Dq)SiR1R2OH] is neutralized with a phosphorus nitride halide such as phosphorus nitride chloride represented by the formula: [X3P(NPX2)nPX3]PX4- (wherein n is 1-6) and subjected to condensation with a hydrogen-contg. organosiloxane represented by the formula: MDHM (wherein M is R4R5R6SiO1/2; and DH is SiR3HO2/2) to give a hydrogenated silicone copolymer represented by the formula: MuDqTrQs (wherein Dq is SiR1R2 O2/2; T is R7SiO3/2; Q is SiO4/2; and R1 to R7 are each H or a 1-40C hydrocarbon group). This copolymer is compounded with a hydrosilylation catalyst to give a curable compsn.