A method for fabricating subminiature, high-performance monolithic duplexer is disclosed. The method comprises depositing and patterning a lower electrode on an upper surface of an insulation layer on a substrate, so as to expose a first part of the insulation layer; depositing a piezoelectric layer on an upper surface of the exposed insulation layer and the lower electrode; depositing a metal on the upper part of the piezoelectric layer and patterning the metal to form a resonance part and a trimming inductor, wherein the lower electrode electrically couples the resonance part and the trimming inductor; fabricating air gap type FBARs (film bulk acoustic resonances) by forming a cavity by etching the substrate under the resonance part; and bonding a packaging substrate on the substrate, the packaging substrate having a phase shifting part which substantially prevents inflow of signal between the air gap type FBARs.