We report on fabrication of ultra-thin GaN membranes of nanometer scale thickness, by using the concept of surface charge lithography based on low-energy ion treatment of the sample surface with subsequent photoelectrochemical etching. The membranes prove to be transparent to both electrons and UV radiation, emit mainly yellow cathodoluminescence, and exhibit electrical conductivity. Successful fabrication of nanometer-thin membranes opens unique possibilities for exploration of two dimensional GaN-based structures predicted to be ferromagnetic with defect-induced half-metallic configuration which is of peculiar importance for spintronics applications.