A thermally conductive composition is a thermally conductive composition including (A) a spherical thermally conductive filler, (B) an alkoxysilane compound or dimethylpolysiloxane, and (C) a polyorganosiloxane (not inclusive of the dimethylpolysiloxane of component (B)), wherein component (A) 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; component (B) and component (C) are included in a total amount of 1.5 to 35 parts by mass relative to 100 parts by mass of component (A); and a content ratio of component (C) in the total amount of component (B) and component (C) is 15 to 98% by mass.