A subminiature, high-performance monolithic duplexer is disclosed. The monolithic duplexer includes a substrate, a transmitting-end filter formed in a first area on an upper surface of the substrate, a receiving-end filter formed in a second area on the upper surface of the substrate, a packaging substrate, 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, 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.