Patterned regrowth of n-GaAs through a Si3N4 mask prepared on molecular beam epitaxy (MBE) grown n-GaAs layers has been explored. An arsenic capping layer was deposited in the MBE growth chamber prior to mask definition, in order to protect the GaAs surface during ex situ processing. Removal of this cap from the lithographically defined mask area was accomplished by hydrogen plasma etching prior to Si3N4 deposition. After in situ thermal desorption of the As cap and phase selective regrowth, the samples were inspected with scanning electron and atomic force microscopy to establish the growth selectivity and examine the surface morphology. Electrolytic carrier profiling and secondary ion mass spectrometry measurements were carried out to characterize the growth-interrupted GaAs-GaAs interface. We find that the surface morphology and defect density of regrown GaAs epilayers are comparable to those of continuously grown epilayers of the same overall thickness. Structuring of the arsenic cap with hydrogen plasma etching and subsequent selective regrowth after decapping can both be achieved on a micrometer length scale. Moreover, this arsenic passivation of the epilayer surface significantly reduces the built-in potential barrier at the regrowth interface (from 0.45 to 0.07 V) and the incorporation of interfacial carbon impurities, compared to regrowth on nonpassivated GaAs surfaces.