More sophisticated III-V devices and the challenge of integration require material growth over structured surfaces. Of particular interest are the Ga-In-As-P materials. Due to the surface selective growth in metalorganic molecular beam epitaxy a high degree of perfection in locally grown structures can be achieved. However, a clear picture of the growth mechanism on various crystal planes and structures helps optimizing the so-called selective area epitaxy. These mechanisms, in respect to relevant epitaxial parameters (V-III-ratio, rate, crystal orientation) with emphasis on lateral butt coupling structures into various crystal directions is discussed. Application of in situ grown lateral heterojunctions for e.g. laser-amplifier waveguide integration are presented.