Gallium arsenide crystals were synthesized by the horizontal Bridgman method in neutron‐activated boats of natural and synthetic fused quartz. Instrumental radiochemical techniques were applied to determine the silicon concentrations from Si31 radioactivity measurements and to identify other trace elements transferred to the gallium arsenide during the process. All crystals were found completely enveloped in an impurity‐enriched surface layer containing silicon concentrations up to 1500 ppm. Bulk concentrations of silicon ranged from , and varied in different sections of the crystals within a factor of 1.7. Evidence of several types of transfer mechanisms was obtained. Other impurities that originated from natural fused quartz and were detected in the form of their radioactive isotopes in the crystals include copper, gallium, antimony, and gold at concentrations below 1016 atoms/cm3; the concentrations of these contaminants were effectively decreased by use of high‐purity synthetic quartz.