We have investigated the effect of thermal annealing on uncapped and Si-capped Pr2O3 films deposited on Si(100) substrate by Auger electron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. A rapid diffusion of Si out of the substrate was found for uncapped films at temperatures starting from 700degreesC. The diffused Si is oxidized, forming a Pr2O3-Pr-x-O-y-Si-z mixture. The excess Si diffuses through the film, forming a SiO2 rich layer on the surface. Annealing of uncapped films in vacuum has qualitatively similar effects as annealing in N-2, which is not the case for Si-capped films. The latter were transformed into a Pr2O3-Pr-x-O-y-Si-z mixture when annealed in N-2 starting from 900degreesC and into PrSix when annealed in vacuum starting from 700degreesC. Two distinct PrSix phases were found, with Si-richer phases corresponding to higher annealing temperature.