A one-part type UV-thickening, heat-conductive silicone grease composition comprising, as essential components, 100 parts by weight of an organopolysiloxane having a viscosity of 50 to 100,000 mPa·s at 25°C and containing at least one silicon-bonded alkenyl group per molecule, an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule having the general formula: wherein R is a C 1 -C 10 monovalent hydrocarbon group free of aliphatic unsaturation and m is an integer of 2 to 200, in such an amount that the number of Si-H groups divided by the number of silicon-bonded alkenyl groups in the composition falls in the range from 0.1 to 5.0, an effective amount of a photoactive platinum complex curing catalyst selected from the group consisting of trimethyl(acetylacetonato)platinum complex, trimethyl(2,4-pentanedionate)platinum complex, trimethyl(3,5-heptanedionate)platinum complex, trimethyl(methylacetoacetate)platinum complex, bis(2,4-pentanedionato)platinum complex, bis(2,4-hexanedionato)platinum complex, bis(2,4-heptanedionato)platinum complex, bis(3,5-heptanedionato)platinum complex, bis(1-phenyl-1,3-butanedionato)platinum complex, bis(1,3-diphenyl-1,3-propanedionato)platinum complex, (1,5-cyclooctadienyl)dimethyl platinum complex, (1,5-cyclooctadienyl)diphenyl platinum complex, (1,5-cyclooctadienyl)dipropyl platinum complex, (2,5-norbornadiene)dimethyl platinum complex, (2,5-norbornadiene)diphenyl platinum complex, (cyclopentadienyl)dimethyl platinum complex, (methylcyclopentadienyl)diethyl platinum complex, (trimethylsilylcyclopentadienyl)diphenyl platinum complex, (methylcycloocta-1,5-dienyl)diethyl platinum complex, (cyclopentadienyl)trimethyl platinum complex, (cyclopentadienyl)ethyldimethyl platinum complex, (cyclopentadienyl)acetyldimethyl platinum complex, (methylcyclopentadienyl)trimethyl platinum complex, (methylcyclopentadienyl)trihexyl platinum complex, (trimethylsilylcyclopentadienyl)trimethyl platinum complex, (dimethylphenylsilylcyclopentadienyl)triphenyl platinum complex, and (cyclopentadienyl)dimethyltrimethylsilylmethyl platinum complex, and 100 to 20,000 parts by weight of a heat-conductive filler having a thermal conductivity of at least 10 W/m·°C, and E) an organopolysiloxane having the general formula: wherein R 1 is independently a substituted or unsubstituted monovalent hydrocarbon group, R 2 is independently an alkyl, alkoxyalkyl, alkenyl or acyl group, n is an integer of 2 to 100, and a is an integer of 1 to 3, in an amount of 5 to 900 parts by weight per 100 parts by weight of component, the composition having a viscosity of 30 to 800 Pa·s at 25°C as measured by a Malcom viscometer at a rotational speed of 10 rpm. 100 parts by weight of an organopolysiloxane having a viscosity of 50 to 100,000 mPa·s at 25°C and containing at least one silicon-bonded alkenyl group per molecule, an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms per molecule having the general formula: wherein R is a C 1 -C 10 monovalent hydrocarbon group free of aliphatic unsaturation and m is an integer of 2 to 200, in such an amount that the number of Si-H groups divided by the number of silicon-bonded alkenyl groups in the composition falls in the range from 0.1 to 5.0, an effective amount of a photoactive platinum complex curing catalyst selected from the group consisting of trimethyl(acetylacetonato)platinum complex, trimethyl(2,4-pentanedionate)platinum complex, trimethyl(3,5-heptanedionate)platinum complex, trimethyl(methylacetoacetate)platinum complex, bis(2,4-pentanedionato)platinum complex, bis(2,4-hexanedionato)platinum complex, bis(2,4-heptanedionato)platinum complex, bis(3,5-heptanedionato)platinum complex, bis(1-phenyl-1,3-butanedionato)platinum complex, bis(1,3-diphenyl-1,3-propanedionato)platinum complex, (1,5-cyclooctadienyl)dimethyl platinum complex, (1,5-cyclooctadienyl)diphenyl platinum complex, (1,5-cyclooctadienyl)dipropyl platinum complex, (2,5-norbornadiene)dimethyl platinum complex, (2,5-norbornadiene)diphenyl platinum complex, (cyclopentadienyl)dimethyl platinum complex, (methylcyclopentadienyl)diethyl platinum complex, (trimethylsilylcyclopentadienyl)diphenyl platinum complex, (methylcycloocta-1,5-dienyl)diethyl platinum complex, (cyclopentadienyl)trimethyl platinum complex, (cyclopentadienyl)ethyldimethyl platinum complex, (cyclopentadienyl)acetyldimethyl platinum complex, (methylcyclopentadienyl)trimethyl platinum complex, (methylcyclopentadienyl)trihexyl platinum complex, (trimethylsilylcyclopentadienyl)trimethyl platinum complex, (dimethylphenylsilylcyclopentadienyl)triphenyl platinum complex, and (cyclopentadienyl)dimethyltrimethylsilylmethyl platinum complex, and 100 to 20,000 parts by weight of a heat-conductive filler having a thermal conductivity of at least 10 W/m·°C, and E) an organopolysiloxane having the general formula: wherein R 1 is independently a substituted or unsubstituted monovalent hydrocarbon group, R 2 is independently an alkyl, alkoxyalkyl, alkenyl or acyl group, n is an integer of 2 to 100, and a is an integer of 1 to 3, in an amount of 5 to 900 parts by weight per 100 parts by weight of component, the composition having a viscosity of 30 to 800 Pa·s at 25°C as measured by a Malcom viscometer at a rotational speed of 10 rpm.