Provided is a silicone composition that has high thermal conductivity and favorable adhesion. A silicone composition that contains (A) 50-99.9 parts by mass of an organopolysiloxane that has at least two aliphatic unsaturated hydrocarbon groups per molecule thereof and has a kinematic viscosity of 60-100,000 mm2/s at 25° C., (B) 0.1-50 parts by mass of a silicone resin that has at least one aliphatic unsaturated hydrocarbon group per molecule thereof (provided that the total of components (A) and (B) is 100 parts by mass), (C) an organohydrogen polysiloxane, (D) 0.01-10.0 parts by mass of an organic peroxide that has a ten-hour half-life temperature of at least 40° C. per 100 total parts by mass of components (A) and (B), and (E) 100-3,000 parts by mass of a thermally conductive filler that has a thermal conductivity of at least 10 W/(m·° C.) per 100 total parts by mass of components (A) and (B).