The possibility of ultra-thin Y2O3 (yttrium sesquioxide) films as insulator of metal ferroelectric insulator semiconductor (MFIS) structure was investigated. The ultra-thin Y2O3 films with thickness of 10-40 nm were fabricated on p-type Si (100) substrates by molecular beam epitaxy(MBE) in vacuum and subsequently submitted to rapid thermal processing (RTP) in air ambient at 700,800 and 900 ℃ for 30 min,respectively. The films were characterized by X-ray diffractometry and Raman spectroscopy. High frequency capacitance-voltage (C—V) characteristics and current-voltage (I—V) characteristics of the Y2O3/Si structure were analyzed. A Raman peak of the Y2O3 thin films was observed at 378 cm-1. From the C—V data,these films exhibit dielectric constants ranging from 13 to 17.28,the hysteresis width (ΔVFB) ranging from 0.07 to 0.22 V and the density of trapped charges ranging from 1.65×1011 to 4.01×1011 cm-2. A leakage current of 4.75×10-8 -9.0×10-6 A/cm2 at 1.5 MV/cm was observed. The results show that the Y2O3 buffer layers are suitable for non-volatile MFIS structure field-effect-transistors (FETs) memory application.