A Pt/SBT/insulator/Si structure for transistor gate materials in metal/ferroelectric/insulator/semiconductor (MFIS) field-effect transistors was fabricated and the electrical properties of the MFIS structure with various insulators were investigated. The C-V characteristics containing capacitance values and memory window widths were affected by varying the annealing temperature and the insulator structure for SBT films used as ferroelectrics. While the memory windows of the MFIS structure with NO was maintained at annealing temperatures above 850 degrees C, the memory window widths of the C-V curves for the MFIS structures using a very thin Al2O3 or SiO2 layer decreased with increasing annealing temperature. It was observed that the C-V curves for the MFIS structure using an Al2O3 inter-dielectric were positively shifted due to negative charge generated in the oxide and the interface. Inter-diffusion between the elements of ferroelectric SBT films and Si was observed in the secondary-ion mass-spectrometry (SIMS) depth profiles of the SBT films annealed at 900 degrees C while sharp interfaces were seen in the profiles of the SBT films annealed at 750 degrees C.