A capacitive effective thickness (CET) value of 1.0 nm has been achieved in atomic layer deposited (ALD) high κ dielectrics HfO2 on In0.53Ga0.47As/InP. The key is a short air exposure under 10 min between removal of the freshly grown semiconductor epilayers and loading to the ALD reactor. This has led to minimal formation of the interfacial layer thickness, as confirmed using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. The measured electrical characteristics of metal-oxide-semiconductor diodes of Au/Ti/HfO2(4.5 nm)/In0.53Ga0.47As showed a low leakage current density of 3.8×10-4 A/cm2 at VFB+1 V, which is about eight orders of magnitudes lower than that of SiO2 with the same CET. The capacitance-voltage curves show an overall κ value of 17–18, a nearly zero flatband shift, and an interfacial density of states Dit of 2×1012 cm-2 eV-1.