Gallium nitride (GaN) is one of the most important wide band gap semiconductor materials in modern technology with even higher expectations for future applications it is ought to play a crucial role. Among this, the growth of lattice and thermally matched GaN substrates for the GaN device technology takes an essential piece. This paper is reporting on the achievements in the ammonothermal growth technique of GaN bulk crystals. Important features specific to the ammonothermal technique are focused on. Although only a few groups (currently <; 10 worldwide) are directly involved in the development of the ammonothermal bulk crystal growth technology, partly due to the extreme technological challenges, tremendous progress over the last decade has recently resulted in the fabrication of 2 inch large, free-standing, single crystalline GaN with excellent structural perfection.