In this study, we demonstrated the effect of electrochemical etching on freestanding GaN (FS-GaN) with convex and concave bowing. FS-GaN substrates were grown by hydride vapor phase epitaxy (HVPE) and then separated by the laser lift-off (LLO) process. Electrochemical etching was applied to the exposed Ga- and N-polar faces of the FS-GaN substrates using C2H2O4 as the electrolyte and high voltage. The N-polar faces on the concave and convex FS-GaN substrates were selectively etched, yielding a nano-porous structure. However, the bowing and strain of the FS-GaN substrates only decreased for the convex type. The electrochemical etching was observed to eliminate a nonhomogeneous layer on the N-polar face. The electrochemical etching caused the convex FS-GaN substrate to be more flat, and its bowing curvature decreased from 0.08 m(-1) to 0.06 m(-1). (C) 2018 The Electrochemical Society.