Surface structure of the free-standing GaN substrates with polar (000-1), non-polar (1-100), (11-20), and semipolar (20-21) surface plane were investigated. Clean polar and non-polar GaN surfaces were prepared by annealing under NH 3 atmosphere. (1x1) diffraction patterns were observed by low-energy electron diffraction (LEED) for both polar and non-polar GaN surfaces. The polar GaN surface was found well-ordered, while the non-polar GaN surfaces were found less ordered with atomic steps on the surface. Polar angle dependences of the photoelecton diffraction (PED) intensities exited by MgKα radiation from N 1s level were analyzed for all the GaN surfaces, aiming to determine the polarities of the GaN surfaces with polar and semipolar crystal orientations.