In this work, it is suggested that upward pulses of fast neutrons, which are produced by energetic intracloud lightning, will form terrestrial gamma-ray flashes (TGFs) through neutron inelastic scattering by atoms in the atmosphere. About 1015 fast neutrons produce gamma-ray photons that compose the TGF pulse in altitude of about 20 km, in good agreement with the altitude of TGF source estimated by Dwyer and Smith [Geophys. Res. Lett. 32, L22804 (2005)].