The initial film growth (2-100 cycles) and the interface evolution of HfO2 thin films on GaAs surfaces were investigated for an atomic layer deposition chemistry that utilizes tetrakis(ethylmethyl) amino hafnium and H2O at 250 degrees C. Starting surfaces include native oxide and HF or NH4OH-etched substrates. X-ray photoelectron spectroscopy shows that deposition on native oxide GaAs surfaces results in the gradual consumption of the arsenic and gallium oxides. Arsenic oxides are easier to remove, leaving some metallic arsenic-arsenic suboxide at the interface. The removal of the gallium oxides is slower, and some residual Ga2O3 and Ga2O are detected after 100 process cycles. High resolution transmission electron microscopy confirms the presence of an almost sharp interface for the 100 cycle (12 nm) film and indicates that the as-deposited film is polycrystalline. The depositions on either HF or NH4OH-etched substrates result in a sharp interface with very little residual gallium oxide and arsenic suboxide present. Rutherford backscattering spectroscopy shows that steady-state growth comparable to that achieved on SiO2 is reached after similar to 20 ALD cycles for all GaAs surfaces; however, high initial surface activity is detected for the etched surfaces.