A single-step method of filling the channels of single-walled carbon nanotubes with the melt of refractory GaSe is proposed and successfully implemented. The filled nanotubes are investigated by optical absorption spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It is found that charge transfer from the nanotube walls to embedded GaSe accompanied by lowering of the Fermi level in nanotubes occurs in the obtained nanocomposite; i.e., acceptor doping of nanotubes takes place.