A film bulk acoustic resonator is fabricated in the following manner. First, a base layer is formed on an insulating substrate. Then, a resonator assembly is formed on the base layer. The resonator assembly includes a first electrode held in contact with the base layer, a second electrode, and a piezoelectric layer held between the first and the second electrodes. Then, a resist layer is formed to cover the resonator assembly and the base layer. Then, a through-hole is formed in the resist layer so that the base layer is exposed via the through-hole. Then, etchant is supplied via the through-hole to make a space in the base layer under the resonator assembly. Finally, the resist layer is removed.