SrBi₂Ta₂O₉ (SBT) films were spin-coated on Pt/Ti/SiO₂/Si, and subsequently annealed by millimeter-wave heating as well as electric furnace one. It was found that remnant polarization of films annealed by millimeter-wave was higher than those by electric furnace heating, and it was attributed to better crystallinity and suppression of formation of non-ferroelectric pyrochlore phase in the millimeter-wave annealing. Enhancement of diffusion by millimeter-wave irradiation is suggested to bring about improvement of crystallinity. Additionally, the Pt layer is considered to be kept at lower temperature due to lower millimeter-wave absorption of Pt, and inter-diffusion among SBT, Pt and Ti layers, which causes formation of non-ferroelectric pyrochlore phase, is inhibited.