We prepared SrBi2Ta2O9(SBT) ferroelectric thin films on SiO2/Si and on MgO buffered SiO2/Si substrates using laser ablation, in situ annealing and postannealing, and observed retention time longer than 7 days. On SiO2/Si substrates, only the samples annealed at 800 °C occasionally exhibited good memory properties. On MgO buffered SiO2/Si substrates, successful probability for finding good measuring dots increased largely even while postannealing temperature was as low as 650 °C; their typical memory window was 3.1 V and retention time over 7 days without serious degradation. The MgO buffer layer inserted between SBT and SiO2/Si may play three positive roles on the quality of metal–ferroelectric–insulator–semiconductor structure: preventing bismuth loss, lowering crystallization temperature, and decreasing leakage current. © 1999 American Institute of Physics.