This paper describes the structural properties and electrical characteristics of thin Yb2O3 gate dielectrics deposited on silicon substrates through reactive sputtering. The structural and morphological features of these films were studied, as a function of the growth conditions (three various argon-to-oxygen flow ratios, 10/15, 15/10, and 20/5, and temperatures from 600 to 800 degrees C), by X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. It was found that Yb2O3 dielectrics having a 15/10 flow condition after annealing at 700 degrees C exhibit a thinner capacitance equivalent thickness and excellent electrical properties, including the interface trap density and the hysteresis in the capacitance-voltage curves. Furthermore, this condition has a small slope in the Poole-Frenkel emission and the Schottky emission, indicating a shallow level trap and a low barrier height in the Yb2O3 film. These results suggest the reduction of the interfacial SiO2 formation and minimal surface roughness due to the optimization of oxygen in the metal-oxide film.