The crystallinity and wet etching behaviors of ultrathin (<10 nm) HfO2 films grown by metal organic chemical vapor deposition (MOCVD) were examined as a function of deposition temperature, film thickness, and post-deposition annealing. Films 3 nm in thickness deposited at 400 or 500 °C were amorphous as-deposited and slowly etchable in aqueous HF; after annealing at 700 °C, the same films showed some nanocrystallinity and were impervious to HF. However, thicker films grown under the same conditions showed significant crystallinity and were impervious to HF even as-deposited. These observations, in combination with measurements on various samples etched back by an Ar+ ion damage/wet etch process, suggest a film structure comprising an initially amorphous near-interface region capped with a HF-resistant crystalline upper layer. It was found that the initially amorphous near-interface region (the bottom 1–3 nm) of films grown at 500 °C can be induced to at least partially crystallize as the upper part of the film starts becoming crystalline as-deposited, but that this near-interface region remains at least partially amorphous after annealing at 700°C.