The (100)-oriented lanthanum hexaboride (LaB6) films, deposited on MgO substrate by e-beam evaporation technique, were oxidated at 400 degrees C, immersed in distilled water, and post-annealed at 650 degrees C in vacuum (3.6 Pa). The results obtained by X-ray diffraction, scanning electron microscope and reflection spectroscopy showed formation of La2O3/LaB6 structure with lanthanum oxide (La2O3) overlayer of cubic phase. The asymmetrical non-linear current-voltage and capacitance-voltage characteristics have been measured on Al/La2O3/LaB6/MgO stack at 1 kHz under bias voltage from -10 to +10 V and explained by space-charge-limited current; the dielectric constant of 11 for as-grown La2O3 is obtained. (C) 2014 Elsevier B.V. All rights reserved.