In this work, a novel half-adder circuit based on nanometric ballistic Y-junctions is demonstrated. The circuit consists of two building blocks with different functionalities. A core structure is built up by a ballistic branching section of a current channel coupled via an internal gate and a tunnel-junction to a second Y-junction. The outputs are amplified by two feedback coupled Y-branch switches. We demonstrate the potential of monolithic integrated nanojunctions as nanoelectronic circuits with high logic functionality and well-defined output levels.