Low-pressure hydride vapor phase epitaxy (HVPE) is being used for the regrowth of thick GaAs on orientation-patterned templates for nonlinear optical frequency conversion. We have achieved epitaxial growth rates of 200 mu m/h and produced millimeter-thick films in 10-h-long growth runs. A critical problem in the HVPE regrowth of orientation-patterned GaAs is the preservation of the original patterned structure-during thick growth, the domain walls often bend and annihilate. Measurements indicated that the domain wall bending decreased as the growth temperature was reduced. The substrate miscut and the orientation of unpatterned regions also affect the vertical propagation of domain walls. In this paper we discuss the process improvements which have facilitated the production of millimeter-thick layers with nearly vertical domain walls. Published by Elsevier B.V.