A kinetic study was done on the decomposition of source materials used in metalorganic vapor phase epitaxy (MOVPE) such as trimethylgallium, trimethylindium, tertiarybutylarsine, tertiarybutylphosphine and dimethylzinc. The purpose of this study was to construct reaction models with accurate rate constants, which are required for the numerical analysis of MOVPE process and computer assisted process optimization. For the measurements we employed a quartz-tube cracking reactor and Fourier transform infrared spectrometer (FT-IR) as the gas monitoring system. First, the decomposition rate of each source was measured and the ability of the system to determine source gas decomposition rates was validated. Next the effect of substrate surfaces on the decomposition rates and the effect of gas mixing were examined. We observed that surface reaction rates were not negligible in the decomposition of some sources, and that the decomposition rates of group III sources increased when they were mixed with group V sources. The results of this study showed that the effect of substrates and gas mixing need to be properly accounted for in numerical models to accurately simulate epitaxial growth process.