The effects of ion implantation on the response to indentation in epitaxially grown hexagonal GaN films were studied by means of the static microindentation technique, utilizing Knoop and Vickers indenter geometries. Mg, O, Au, Xe and Ar ions were used as projectiles for the implantation process. Heavily damaged polycrystalline epilayers showed enhanced microhardness values and normal indentation size effect (ISE). Amorphised epilayers showed lower microhardness values, while they presented reverse ISE. The shape of the Knoop indentation print as a function of the implanted species revealed that reverse ISE is connected with plastic behavior. Implantation was also found to render films more receptive to fracture. Normal ISE curves were explained using models such as Meyer's law, Hays-Kendall approach, proportional specimen resistance (PSR), modified PSR and elastic/plastic deformation (EPD) models. (c) 2006 Elsevier B.V. All rights reserved.