The origins of formation of two not yet completely understood structural defects in undoped semiconductor compound crystals, mainly GaAs, are analysed and discussed-(i) dislocation patterning in cells and (ii) dislocation bunching. The dependences of the mean cell diameter d oil the dislocation density N and acting thermo-mechanical stress sigma in VCz GaAs crystals are investigated and compared with metallic crystals. The rules of correspondence d similar to Nb-1/2 and d similar to Gbsigma(-1) (G-shear modulus, b-Burgers vector) have been confirmed. The superposition of two genesis paths is proposed: formation of dislocation networks by dynamical polygonization and cell patterning by dissipative structuring. Possible reasons for the absence of missing of cells in InP crystals are proposed. The concepts of dislocation bunching are reviewed. Newer simulation results in the field of metals demonstrate the possible importance of oscillating growth conditions like melt convection, turbulences or heating temperature fluctuations. Experimentally, the probability of appearance of dislocation bundles in VCz GaAs crystals as function of the growing interface shape is investigated. Considering the radial distribution of von Mises tensors a bunching by glide collision is possible. (C) 2004 Elsevier B.V. All rights reserved.