Abstract: An improved high performance semiconductor package assembly for interconnecting a plurality of integrated circuit devices having a multilayer substrate with internal wiring including signal wiring and external signal and power connections, a plurality of integrated circuit semiconductor devices supported on the top surface of substrate in electrically connected operative relation, the improvement being a power supply distribution system for providing electrical supply voltages to the devices from the power connections consisting of radial waveguide structure including parallel waveguide planes with a low input impedence to reduce switching noise, the waveguide planes located between the signal fan-out wiring and internal wiring metallurgy and connected in common to all of the plurality of devices.