We investigated the interfacial reaction between ICB deposited Y2O3 film and chemically oxidized (100) silicon substrates upon annealing in Ar and O-2 gas ambients using transmission electron microscopy (TEM) and X-ray diffractometry (XRD), We observed the growth of the SiO2 layer between the Y2O3 films and the Si substrate after annealing treatments in O-2 gas and Ar gas ambients. The growth of the SiO2 layer is due to the diffusion of the oxygen species through Y2O3 films, and subsequent reaction with the silicon substrates. We also found that yttrium silicate layer is formed between the SiO2 layer and Y2O3 films upon annealing treatments.