To provide an interlayer filler composition which, in 3D lamination of semiconductor device chips, forms a highly thermally conductive filling interlayer simultaneously with the bonding of solder bumps or the like and lands between semiconductor device chips, a coating fluid and a process for producing a three-dimensional integrated circuit.An interlayer filler composition for a three-dimensional integrated circuit, which comprises a resin (A) having a melt viscosity at 120° C. of at most 100 Pa·s and a flux (B), the content of the flux (B) being at least 0.1 part by weight and at most 10 parts by weight per 100 parts by weight of the resin (A).