This book constitutes the refereed proceedings of the 5th International Symposium on High-Performance Computing, ISHPC 2003, held in Tokyo-Odaiba, Japan in October 2003.The 23 revised full papers and 16 short papers presented together with 4 invited papers and 7 refereed papers accepted for a concurrently held workshop on OpenMP (WOMPEI 2003) were carefully reviewed and selected from 58 submissions. The papers are organized in topical sections on architecture, software, applications, and ITBL.