Zinc selenide is attractive for numerous optical applications in the mid and longwave infrared from solid state lasers to non-linear optical frequency conversion. Its use has been limited by the availability of single crystal and epitaxial materials. To meet these challenges we have developed a low-pressure hydride vapor phase epitaxy (HVPE) process for growth of high quality thick ZnSe layers on GaAs (1 0 0) vicinal and orientation-patterned GaAs (OP-GaAs) substrates. We show growth of > 300 mu m thick layers at growth rates > 50 mu m/hr. With only 0.26% lattice mismatch between ZnSe and GaAs, epitaxial layers with crystal quality comparable to bulk ZnSe substrates are achieved. X-ray reciprocal space maps show the ZnSe to be fully relaxed. Cross-sectional TEM imaging analysis shows stacking faults at the interface that propagate in to the growing film consistent with a full relaxed film. Surface morphology shows the presence of pits that have their long axis perpendicular to [1-10] direction. Low temperature photoluminescence reveals band to band emission that consisted of the 2.797 eV direct band gap along with the strong exciton emission at 2.802 eV. Growth on OP templates revealed low fidelity domains of thickness > 50 mu m. This work presents a process to produce high quality thick layers potentially suitable for laser and frequency conversion for defense and civilian applications.