Unintentionally doped impurities in AlxGa1-xAs grown with trimethylgallium (TMG), trimethylaluminum (TMA). and arsine (AsH3) were studied using a low-pressure disk-rotating metal-organic vapor-phase epitaxy (MOVPE) system. It was found that the growth temperature and AsH3 flow rate dependency of the carbon concentration is almost the same as that of the residual carrier concentration. The hydrogen concentration was also found to have a similar relationship to the carbon concentration. On the other hand, the oxygen concentration did not show such a trend. This means that the oxygen incorporation pathway is different from that of carbon and hydrogen. The impurity incorporation mechanisms in AlxGa1-xAs are very complicated and depend on the growth temperature and the supply rate of TMA and AsH3.