Silicone composition comprising: 5 to 99 parts by weight of organopolysiloxane having a kinematic viscosity at 25°C of 10 to 10,000 mm 2 /s as measured with an Ostwald viscometer and represented by the following general formula: wherein each R 1 independently is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, each R 2 independently is alkyl, alkoxyalkyl, alkenyl, or acyl, a is an integer of 5 to 100, and b is an integer of 1 to 3; 95 to 1 parts by weight of organopolysiloxane having a kinematic viscosity at 25°C of 10 to 100,000 mm 2 /s as measured with an Ostwald viscometer and represented by the following general formula: R 3 c SiO (4-c)/2 wherein each R 3 independently is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, and c is a number of 1.8 to 2.2, provided that the total amount of components and combined is 100 parts by weight; α-aluminum oxide powder, the α-aluminum oxide having a purity of 99% or more, a crystal structure of a hexagonal close-packed lattice formed of a polyhedron with 8 or more faces, and a particle shape with a D/H ratio of 0.3 to 30, where a maximum particle diameter parallel to a hexagonal lattice face of the hexagonal close-packed lattice is taken as D and a particle diameter perpendicular to the hexagonal lattice face is taken as H, and the α-aluminum oxide powder having an average particle diameter of 0.3 to 5 μm, the proportion of coarse particles of 10 μm or more being 1% by weight or less of the entire component in a laser diffraction-type particle size distribution when measured as disclosed in the description, and spherical and/or irregular-shaped zinc oxide powder having an average particle diameter of 0.01 μm or more and less than 3 μm, the proportion of coarse particles of 10 μm or more being 1% by weight or less of the entire component in a laser diffraction-type particle size distribution when measured as disclosed in the description; provided that a weight ratio of component and component is 5/5 to 9.5/0.5, and the total amount of components and combined is 65 to 80% by volume of the entire composition, the composition having a heat conductivity of 2 W/m·K or more and less than 4 W/m·K as measured by a hot disk method in accordance with ISO 22007-2, and a viscosity at 25°C of 5 to 800 Pa·s as measured by a spiral viscometer at a rotation speed of 10 rpm. 5 to 99 parts by weight of organopolysiloxane having a kinematic viscosity at 25°C of 10 to 10,000 mm 2 /s as measured with an Ostwald viscometer and represented by the following general formula: wherein each R 1 independently is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, each R 2 independently is alkyl, alkoxyalkyl, alkenyl, or acyl, a is an integer of 5 to 100, and b is an integer of 1 to 3; 95 to 1 parts by weight of organopolysiloxane having a kinematic viscosity at 25°C of 10 to 100,000 mm 2 /s as measured with an Ostwald viscometer and represented by the following general formula: R 3 c SiO (4-c)/2 wherein each R 3 independently is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 18 carbon atoms, and c is a number of 1.8 to 2.2, provided that the total amount of components and combined is 100 parts by weight; α-aluminum oxide powder, the α-aluminum oxide having a purity of 99% or more, a crystal structure of a hexagonal close-packed lattice formed of a polyhedron with 8 or more faces, and a particle shape with a D/H ratio of 0.3 to 30, where a maximum particle diameter parallel to a hexagonal lattice face of the hexagonal close-packed lattice is taken as D and a particle diameter perpendicular to the hexagonal lattice face is taken as H, and the α-aluminum oxide powder having an average particle diameter of 0.3 to 5 μm, the proportion of coarse particles of 10 μm or more being 1% by weight or less of the entire component in a laser diffraction-type particle size distribution when measured as disclosed in the description, and spherical and/or irregular-shaped zinc oxide powder having an average particle diameter of 0.01 μm or more and less than 3 μm, the proportion of coarse particles of 10 μm or more being 1% by weight or less of the entire component in a laser diffraction-type particle size distribution when measured as disclosed in the description; provided that a weight ratio of component and component is 5/5 to 9.5/0.5, and the total amount of components and combined is 65 to 80% by volume of the entire composition, the composition having a heat conductivity of 2 W/m·K or more and less than 4 W/m·K as measured by a hot disk method in accordance with ISO 22007-2, and a viscosity at 25°C of 5 to 800 Pa·s as measured by a spiral viscometer at a rotation speed of 10 rpm.