A dislocation-eliminating chemical control method for high-quality GaN nanostructures together with various types of InGaN quantum well structures are demonstrated using a chemical vapor-phase etching technique. Unlike chemical wet etching, chemical vapor-phase etching could efficiently control the GaN and form various shapes of dislocation-free and strain-relaxed GaN nanostructures. The chemically controlled GaN nanostructures showed improved crystal quality due to the selective etching of defects and revealed various facets with reduced residual strain via the facet-selective etching mechanism. These structural properties derived excellent optical performance of the GaN nanostructures. The chemical vapor-phase etching method also showed possibilities of the fascinating applications for high-efficiency InGaN quantum well structures, such as InGaN quantum well layer on void embedded GaN layer, InGaN quantum well embedded GaN nanostructure, and InGaN/GaN core/shell nanostructure.