High purity AsH 3 has long been demanded in the application of vapor phase epitaxy of III–V compounds. To this end, a new inner surface treatment of an aluminum cylinder and a novel catalyst (MN purificator™) for purification of AsH 3 were developed. The inner surface of the aluminum cylinder was smoothed and washed with a high pressure de-ionized water. Auger analysis showed that a clean oxide layer was formed on the inner surface of the aluminum cylinder after the new treatment. A trace moisture analyzer by means of quartz oscilation frequency showed that the water concentration was less than 10 ppb in AsH 3 filled in the new aluminum cylinder, whereas the water concentration for the conventional cylinder was 300 ppb. The MN purificator™ decomposed SiH 4 at room temperature, but had no effects on AsH 3. With AsH 3 purified with MN purificator™ and filled in the new aluminum cylinder, high resistivity P-type GaAs layers were reproducibly grown by MOVPE at AsH 3/TMG ratio up to 100, where N-type layers were usually obtained.