Dual-type octahedral void defects were found in Czochralski silicon in 1995. This was a trigger for a "renaissance" in the field of Si crystal investigation as well as a breakthrough toward the new stage of the next-generation Si-microelectronics development. Crystallographically each void is basically composed of eight sub-planes of (1 1 1), but it is often truncated by a (0 0 1) sub-plane in the crystal-growth direction. This is a clear characterization of void detects and is closely related to some physical phenomenon in Si melt growth. This paper characterizes the occurrence of (0 0 1) sub-planes in void defects. (C) 2002 Elsevier Science B.V. All rights reserved.