We studied microscopic chemistry of gaseous phase in GaN growth by computational thermodynamic analysis of metalorganic vapor phase epitaxy with two- and three-flow methods. Correlations between quality of GaN layers and gaseous phase chemistry were found from the computational analysis. It was confirmed that laminar flow, on a substrate during growth was necessary to obtain a high-quality GaN layer in spite of high growth temperature. Optimum decomposed-species V/III ratio (NH2/GaCH3) were considered in the range of 1000-2000 to achieve high electron mobility more than 200 cm(2)/V s. Two-flow method was easier to achieve the optimum condition than three-flow method both in experiments and in computational analysis. (C) 2002 Elsevier Science B.V. All rights reserved.