The knowledge of the structure of dislocations in semiconductors is of importance for an understanding of their mechanical and electrical properties. In electronic devices dislocations are known to act as recombination centers for charge carriers and as traps for impurity atoms. In addition dislocations play an important role in the mechanical relaxation of elastic stresses in lattice-mismatched heterostructures. In Si-based epitactical heterostructures alloys of Si and Ge are used to adjust the lattice parameters by variation of the alloy composition thereby modifying the elastic stresses in a controlled manner. Such strained layer structures are of potential application for electronic components with improved performance.We have investigated dislocations in SixGe1-x crystals grown from the melt by the Czochralski and Bridgman method, respectively. The dissociation of dislocations into Shockley partials in SixGe1-x. alloys with low (x ≈ 0.05) and high (x ≈ 0.5) Si content was characterized by analytical electron microscopy at 300 kV.