The grown-in defects in Czochralski silicon crystals have been well known as a void-type shape. Recently. it has been reported that in nitrogen-doped silicon crystals the grown-in defects are formed in some different shapes. The density of these defects in nitrogen-doped silicon crystals is remarkably higher than that of Czochralski silicon crystals. We study the morphology of grown-in defects and the morphological change of grown-in defects on annealing in nitrogen-doped silicon crystals with transmission electron microscopy. This showed that there is one kind of nitride precipitate in nitrogen-doped silicon crystals. The growth of whisker-like defects is identified in nitrogen-doped silicon crystals after hydrogen annealing. Nitrogen and oxygen are detected from these whisker-like defects. The whisker-like defects contain both a distorted diamond structure and an amorphous structure that was clarified by the high-resolution transmission electron microscopic images. (C) 2002 Elsevier Science B.V. All rights reserved.