The structural distribution, surface composition and bonding states of HCl- and Na2Se/NH4OH-treated GaAs surfaces were investigated using angle-resolved X-ray photoelectron spectroscopy and low energy electron diffraction (LEED). The passivated GaAs surface by Na2Se/NH4OH solution showed a formation of As-Se bond. Compared with HCl-treatment, more pronounced oscillation of photoelectron intensities of Ga and As was observed with the Na2Se/NH4OH-treated GaAs surface according to the polar angle of GaAs surface. Through LEED analysis, the passivated GaAs surface showed a (2 x 1)-reconstructed structure with regular distribution of As-Se bonds. After in situ annealing under ultra high vacuum condition, bond exchange from As-Se to Ga-Se occurred. After annealing, Se also showed pronounced oscillation of photoelectron intensity according to the polar angle of GaAs. This could be explained by the anion exchange reaction of Se with As in the lattice site or by the occupation of As vacant site formed during annealing to a depth of three atomic layers.