Crystalline thin films of Gd2O3 of varying thicknesses were grown on 2 inch p-Si(1 0 0) wafers by H2O-assisted atomic layer deposition (ALD) using a homoleptic gadolinium tris-guanidinate precursor [Gd(iPr-Me2N-Guan)3]. The Gd 2O3 layers grown at 225 °C were polycrystalline with columnar growth morphology. The as-grown films were electrically characterized as a metal oxide semiconductor (MOS) capacitor and exhibited instability in the flat-band voltage. Upon subjection to post-deposition defect-passivation treatment, they exhibited promising electrical characteristics. More importantly, the vertical downscaling of Gd2O3 thin films through the H2O-assisted ALD process could be realized through the capacitance equivalent thickness versus physical thickness studies. © 2010 IOP Publishing Ltd.