We have studied the impact of atomic-layer-deposition (ALD) temperature on the HfO2/InGaAs metal-oxide-semiconductor (MOS) interface with a comparison to the Al2O3/InGaAs interface. It is found that the interface properties such as the C-V characteristics and the interface trap density (Dit) and the interface structure of HfO2/InGaAs have strong dependence on the ALD temperature, while the Al2O3/InGaAs interfaces hardly depend on it. As a result, we have achieved the HfO2/InGaAs interfaces with low Dit comparable to that in the Al2O3/InGaAs interface by lowering the ALD temperature down to 200 °C or less. Also, we have found that As2O3 and Ga2O3 formed at the interface during ALD increase with a decrease in the ALD temperature. Combined with the ALD temperature dependence of the electrical characteristics, the better C-V characteristics and the lower Dit obtained at the lower ALD temperature can be explained by the As2O3 and Ga2O3 passivation of the HfO2/InGaAs interfaces, which is consistent with a reported theoretical result on the effective passivation of III-V MOS interfaces by trivalent oxides.