We have grown epitaxial grain boundaries of CuGaSe2 by metal organic vapour phase epitaxy onto a GaAs substrate containing a Sigma 3 grain boundary. SEM micrographs show a dense grain boundary. TEM micrographs prove that the grain boundary in the film is the direct continuation of the grain boundary in the substrate. HRTEM shows that the grain boundary in the film is a twin as well and thus a Sigma 3 boundary. Thus, by using a Sigma 3 grain boundary in the cubic GaAs substrate as a template a Sigma 3 grain boundary is obtained in the tetragonal CuGaSe2 film. Kelvin Probe Force Microscopy gives no indication of a space charge around this grain boundary, while in Hall measurements a small barrier of a few 10 meV is evident. This is an experimental indication for the existence of neutral grain boundaries as predicted theoretically. (C) 2007 Elsevier B.V. All rights reserved.