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The results of basic ammonothermal crystallization of gallium nitride are described. The material is mainly analyzed in terms of the formation of stress (called stress-induced polarization effect) and defects (threading dislocations) appearing due to a stress relaxation process. Gallium nitride grown in different positions of the crystallization zone is examined in cross-polarized light. Interfaces between native ammonothermal seeds and new-grown gallium nitride layers are investigated in ultraviolet light. The etch pit densities in the seeds and the layers is determined and compared. Based on the obtained results a model of stress and defect formation is presented. New solutions for improving the structural quality of basic ammonothermal gallium nitride crystals are proposed.