We have developed a prototype network switch, RHiNET-3/SW, for a RHiNET high-performance distributed parallel computing environment. It has eight I/O ports and each port provides high-speed, bi-directional 10-Gbit/s-per-port parallel optical data transmission in a distance of over 300 m. The aggregate throughput is 80 Gbit/s per board. A switch consists of a one-chip CMOS ASIC 8x8 switch LSI (SW-LSI; a 784-pin BGA package), four deskew LSIs, and eight pairs of 1.25-Gbit/s x 12-channel optical interconnection modules on a single board. The switch uses a hop-by-hop retransmission mechanism and credit-based flow control to provide reliable and long-transmission-distance data communication. The deskew LSI has a skew compensation function for 10-bit parallel data channels and an 8B10B encoder/decoder. Its optical transmitter modules use an 850-nm VCSEL and a 12-channel MMF (multi-mode fiber) ribbon. RHiNET-3/SW enables high-throughput. Long-distance and flexible-flow-control network communication by means of distributed parallel computing using commercial PCs.