AbstractFor extensive proliferation of multimedia communications, high‐speed, large‐capacity node systems are required in addition to the technologies for transmission and access systems. Although the performance of the node system has progressed along with the technical advances of LSI, the LSI interconnection is now a bottleneck due to rapid advances in technology, and consequently this bottleneck may limit the performance of the node system. One way to resolve this situation and extract the performance of the LSI at the maximum is the multichip module (MCM) technology. Using this technology, high‐speed, multiply parallel signal transmission can be realized within MCM. However, the input and output of the signal to this MCM still suffers from bottlenecks in terms of connection distance, cable physical volume, transmission speed, flexibility, and antinoise properties so long as the conventional electric I/O is used. In order to resolve this interconnect bottleneck, the authors have developed an optical I/O interface ATM switch MCM in which the optical signal can directly enter and exit the MCM. This module is realized with 0.25‐μm CMOS LSI technology, 40‐layer ceramic MCM technology, ultra parallel optical interconnection technology and cooling technology. The size is 220 × 174 × 15 mm3 and the switch throughput is 80 Gb/s. The optical I/O interface ATM switch MCM developed here is bookshelf installed in a rack and its fundamental operations are confirmed. © 2001 Scripta Technica, Electron Comm Jpn Pt 1, 85(2): 61–68, 2002