The crystallization process in SbxGe1−xalloy films has been observed duringinsituannealing in a transmission electron microscope. Results are presented for two films withx=0.89 (89 at. % Sb) andx=0.71 (71 at. % Sb), which lie on either side of the eutectic composition (x=0.85). In the former films radial crystals are observed to grow rapidly from discrete nuclei, whereas in the latter films the crystallization process occurs through a near‐planar front. In addition, quantitative data obtained from these experiments show that the Sb0.89Ge0.11films have a higher activation energy for crystal growth and a lower temperature for the nucleation of crystals. Significant differences are observed between the crystallization processes for the two films studied, with the Sb0.89Ge0.11film showing better potential for development as an ultrafast optical phase‐change storage medium. ©1995 American Institute of Physics.