The performance of semiconductor films is influenced by the purity of the metal-organic (MO) gas that is used, so it is important to investigate the decomposition behavior of MO gases. The decomposition of dimethylzinc, trimethylgallium and trimethylaluminum is found to depend on the metal surface in the reactor tube. A reactor tube with an Al2O3 surface exhibits the highest temperature as which decomposition of the MO gases started, and the highest activation energy. These results indicate that the Al 2O3 surface has the lowest catalytic activity for the decomposition of these MO gases. However, decomposition of dimethylzinc occurs at room temperature when it is trapped in a reactor tube. This decomposition ceases past a certain trapped time, so the catalytic activity for the decomposition of MO gases by surfaces stabilizes. Therefore, Al 2O3 surfaces are useful for application in MO gas distribution systems.