In this study, an area-selective metal-organic vapor-phase epitaxy (MOVPE) for trench-confined InP-based epitaxial regrowth in-between arrayed rectangular-shaped device elements is reported. Test structures are fabricated to investigate the influence of MOVPE growth and other processing parameters on regrowth control, doping incorporation, and morphology. For correctly chosen crystallographic mesa orientation and mask geometry, good control of growth selectivity, layer morphology, and doping concentration can be achieved, although with an enhanced and non-constant growth rate. This is discussed in terms of orientation-dependent growth rate and loading effects. In addition, a selective etch and regrowth approach which allows for the processing of field-effect transistors of significance for spatial light modulators with trench-integrated driver electronics is successfully implemented.