Ex situ sulfide and HCl wet chemical treatments in conjunction with in situ trimethyl aluminum (TMA) pretreatment were performed before the deposition of Al2O3 on n-InAs surfaces. X-ray photoelectron spectroscopy analyses show a significant reduction of InAs native oxides after different treatments. The capacitancevoltage C-V characterization of Al2O 3/n-InAs structures shows that the frequency dispersion in the accumulation regime is small (< 0.75%/dec) and does not seem to be significantly affected by the different surface treatments, whereas the latter improves depletion and inversion behaviors of the n-channel metaloxidesemiconductor capacitors. The interface trap density profiles extracted from the simulation mainly show donorlike interface states inside the InAs band gap and in the lower part of the conduction band. The donorlike traps inside the InAs band gap and in the lower part of the conduction band were significantly reduced by using wet-chemical-plus-TMA treatments, in agreement with C-V characteristics.