The crystal growth of gallium nitride has been investigated by using the ammonolysis of gallium suboxide, the sublimation of gallium nitride or gallium oxide in an ammonia atmosphere, and the ammonolysis of gallium monochloride at 1150° ± 20°C in gas flow systems. The first two techniques have produced only low resistivity gallium nitride crystals of millimeter size. The ammonolysis of gallium monochloride is most promising; single crystals of gallium nitride as large as 25 × 15 × 5 mm, heretofore unknown, have been obtained by using sapphire platelets with main faces of (1 02) orientation as substrates. The single crystallinity of these crystals was verified by chemical etching and optical microscopy and x‐ray diffraction techniques. These crystals, with an electron concentration of about 1010 cm−3 and Hall mobilities of about 150 cm2 V−1 sec−1 at room temperature, have been used as substrates for the growth of large gallium nitride crystals of improved structural perfection.