Synchrotron X-ray transmission topography has been used to study different types of dislocation bundle in 2-inch diameter, (0 0 1) oriented GaAs substrates after growth of a variety of heteroepitaxial III-V compound semiconductor structures. The dislocation bundles of the majority type start at the sample edges in regions of up to about +/-25 degrees around the four <1 0 0> peripheral areas, glide typically up to about 1.5 cm into the bulk of the wafer following +/- [1 1 0] and +/- [1 (1) over bar 0] line directions and form, depending on the dopant type, pseudo-symmetric four- or two-fold sets. The dislocation bundles were observed in samples that were grown in three different makes of molecular beam epitaxy machine. Eradication of the bundles was achieved by modifications to the sample holder of an MBE machine built at the Defence Evaluation and Research Agency, Great Malvern, UK.