Nanostructured GaN surfaces sputtered with Au provide very promising and reproducible platforms for surface enhanced Raman scattering (SERS). The enhancement factor (EF) in SERS is expected to depend strongly on the local metal (Au) surface structure (size, distribution and morphology). Herein we show how temperature -induced coalescence followed by recrystallization of Au on GaN nano -columns occurs well below the melting point of gold. This process is reflected in SEM, TEM images and SERS spectra of Au/GaN - bound p-mercaptobenzoic acid (4 -MBA), a model Raman scatterer. SERS signals of 4 -MBA bound to Au/GaN reach minimum for platforms exposed to t = 350 degrees C before regaining the intensity when annealed in the range of 450-900 degrees C. The results have been discussed in the light of the nature of SERS active sites - so called "hot spots" and structure of Au nanoparticles. (C) 2016 Elsevier B.V. All rights reserved.