Abstract: The polarity of GaN grown by RF-plasma MBE was investigated at different growth temperatures of buffer layer. There are two types of polarities of wurtzite-GaN: Ga-polar and N-polar.The former has greater chemical stability than the latter. Compared with morphology from AFM of GaN samples etched by photo-assisted wet etching, it is found that the N-pol ar GaN is obtained at higher growth temperatures of buffer layer, while buffer layer grown at lower temperatures results in the Ga-polar.