A thermally conductive composition comprising a spherical thermally conductive filler and an alkoxysilane compound represented by the general formula (II-1) or (II-2), wherein x = 10 to 500, and Y = Si(CH 3) 2 CH=CH 2 or Si(CH 3) 3 wherein component is a mixture formulated with specific ratios of fillers having different average particle sizes, the mixture being formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass or more; and component, the alkoxysilane compound, is included in an amount of 0.01 to 20 parts by mass relative to 100 parts by mass of component, wherein the spherical thermally conductive filler of component is a mixture formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass to 60% by mass; and a filler having an average particle size of 40 μm or less in an amount of 15% by mass to 30% by mass; and a filler having an average particle size of less than 8 μm as a balance (in total, 100% by mass); and wherein further the spherical thermally conductive filler of component is selected from metal oxide powders and metal powders. a spherical thermally conductive filler and an alkoxysilane compound represented by the general formula (II-1) or (II-2), wherein x = 10 to 500, and Y = Si(CH 3) 2 CH=CH 2 or Si(CH 3) 3 wherein component is a mixture formulated with specific ratios of fillers having different average particle sizes, the mixture being formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass or more; and component, the alkoxysilane compound, is included in an amount of 0.01 to 20 parts by mass relative to 100 parts by mass of component, wherein the spherical thermally conductive filler of component is a mixture formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass to 60% by mass; and a filler having an average particle size of 40 μm or less in an amount of 15% by mass to 30% by mass; and a filler having an average particle size of less than 8 μm as a balance (in total, 100% by mass); and wherein further the spherical thermally conductive filler of component is selected from metal oxide powders and metal powders. x = 10 to 500, and Y = Si(CH 3) 2 CH=CH 2 or Si(CH 3) 3 wherein component is a mixture formulated with specific ratios of fillers having different average particle sizes, the mixture being formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass or more; and component, the alkoxysilane compound, is included in an amount of 0.01 to 20 parts by mass relative to 100 parts by mass of component, wherein the spherical thermally conductive filler of component is a mixture formulated with a filler having an average particle size of 50 μm or more in an amount of 30% by mass to 60% by mass; and a filler having an average particle size of 40 μm or less in an amount of 15% by mass to 30% by mass; and a filler having an average particle size of less than 8 μm as a balance (in total, 100% by mass); and wherein further the spherical thermally conductive filler of component is selected from metal oxide powders and metal powders.