A subminiature, high-performance monolithic duplexer is disclosed. The monolithic duplexer includes a substrate (100), a transmitting-end filter (300) formed in a first area on an upper surface of the substrate, a receiving-end filter (400) formed in a second area on the upper surface of the substrate, a packaging substrate (200), bonded on an area on the upper surface of the substrate, for packaging the transmitting-end filter and the receiving-end filter in a sealed state, and a phase shifter (210), formed on one surface of the packaging substrate and connected to the transmitting-end filter and the receiving-end filter, respectively, for intercepting a signal inflow between the transmitting-end filter and the receiving-end filter.