The mask-less epitaxial lateral overgrowth of GaN on structured Si(111) substrates was studied by using transmission electron microscopy and photo-electrochemical etching. Structured Si substrates were prepared by using photolithography and dry etching. Here, 4μm-deep holes of 1.5μm diameter, each separated by 2.5μm, were etched into the (111) Si surface. Growth was started by depositing a 10nm-thick AlN buffer layer at 850C, followed by growth (at 1170C) of the GaN epilayer. The deposition of GaN took place firstly on the Si(111) surface, covered with AlN, between the holes. No deposits formed in the holes. During growth, the GaN layer extended vertically and laterally over the holes, up to complete coalescence. Transmission electron microscopy showed that regions over the holes contained only dislocations in the basal plane, resulting from the bending of dislocations nucleated at the Si/AlN interface and at the coalescence boundary between the 2 laterally overgrown layers. This resulted in a marked decrease in dislocation density in those areas of the film. The revelation of dislocations was also achieved by photo-electrochemical etching.