Disclosed is a method of manufacturing a GaN-based material having high thermal conductivity. A gallium nitride-based material is grown by HVPE (Hydride Vapor Phase Epitaxial Growth) by supplying a carrier gas (G1) containing H2 gas, GaCl gas (G2), and NH3 gas (G3) to a reaction chamber (10), and setting the growth temperature at 900 (° C.) (inclusive) to 1,200 (° C.) (inclusive), the growth pressure at 8.08×104 (Pa) (inclusive) to 1.21×105 (Pa) (inclusive), the partial pressure of the GaCl gas (G2) at 1.0×104 (Pa) (inclusive) to 1.0×104 (Pa) (inclusive), and the partial pressure of the NH3 gas (G3) at 9.1×102 (Pa) (inclusive) to 2.0×104 (Pa) (inclusive).