Abstract: A process that, without doping of PBN crucibles, produces semi-insulating GaAs having low, or essentially no, dislocation density; and in which the crystal may be in situ annealed after growth. The process is a variant of the Heat Exchanger Method (HEM) disclosed in U.S. Pat. No. 3,898,051. Crack-free, semi-insulating GaAs crystals having low dislocation density are grown from presynthesized undoped GaAs meltstock in sealed quartz (vitreous silica) crucibles, without the need for an encapsulant. One aspect of the invention features seeded growth of <100> orientation crystals having a dislocation density 1-2 orders of magnitude less than that of the seed; in another aspect, crystals having fewer than 500 dislocations/cam.sup.2 in their center column are grown without a seed.