This paper describes the architecture of a third-generation switching element which may appear in future IBM RS/6000 SP interconnection networks. In this paper this ASIC will be referred as the Switch3 switch chip. Like its predecessors, Switch3 is an 8-port device implementing output-queuing using the high-utilization central-buffering technique. However, Switch3 offers significant enhancements over these existing SP switch chips by incorporating advances in both VLSI technology and in recent interconnection network research. Switch3 introduces a new form of adaptive routing with the potential to significantly improve network bandwidth. It also offers support for collective communication via a powerful hardware multicast replication capability. The technology advances allow link bandwidth to be improved to 500 MB/s per direction per link, and allow the central buffer size to be doubled compared to the current SP switch. Furthermore, the larger Switch3 input buffers are capable of supporting link lengths of up to 100 meters, enabling richly-connected, scalable topologies with a high aggregate bandwidth. Finally, Switch3 offers a number of other significant enhancements including limited support for high-priority traffic and detailed performance monitoring information.