Features of defect formation upon the decomposition of a supersaturated solid solution of a transition metal in silicon were studied. Zinc was used as the transition metal impurity. The silicon was doped with zinc by high-temperature diffusion annealing with subsequent quenching. Microstructures of this material were studied by electron diffraction and high-resolution X-ray transmission electron microscopy combined with X-ray energy-dispersion microanalysis. It was established that the studied material was a quite perfect single crystal but contained chaotically distributed dislocations.