Piezoelectric properties of quartz and quartz-like materials are strongly related to the impurity content in the crystals and, more especially, to their hydroxyl group (-OH) content. This work has been devoted to the determination of the spatial distribution of this impurity in as-grown crystals of gallium phosphate, GaPO4. The investigation was undertaken by infrared spectroscopy from eight samples with different growth conditions and completed by thermally stimulated current/relaxation map analysis techniques. The results allow the best growth parameters to be defined, leading to crystals with the lowest -OH impurity content.