We studied chemical reactions in the metalorganic vapor-phase epitaxial growth of InGaN from the TMGa/TMIn/NH3/H2/N2 system. It was found that the InGaN growth has three main pathways: pyrolysis of TMGa:NH3 adducts; pyrolysis of TMIn; and pyrolysis of NH3 molecules. The InGaN simulations indicated good agreement with the experiments in temperature-dependences of growth rate and composition by considering atomic In re-evaporation. The simulation result showed that our thinner flow channel method could produce more condensed NH2 and In-atom concentrations compared with conventional technology. Therefore, we could raise InGaN growth temperature with the same In content by the thinner flow channel. Since the higher growth temperature can realize the higher quality of InGaN, we have succeeded to fabricate InGaN LEDs in the range from green to deep red by using the 5-mm flow channel.