The etching experiments for n-GaN were done using the wet chemical, photo-enhanced-chemical and electro-chemical etching methods. The experimental results show that n-GaN is etched is diluted NaOH solution at room temperature and the removed thickness of n-GaN is linearly increased with etching times. The etching rate of the photo-enhanced-chemical and electro-chemical etching methods are several times higher than that of the wet chemical method. The maximum etching rate of n-GaN with $n{fallingdotseq}1{ imes}10^{19}cm^{-3}$ was 164 $AA$/min under the experimental condition of the Photo-enhanced-chemical etching. The etching rates of n-GaN are very much dependant on the electron concentrations of the samples. The pattern is $100{mu}m{ imes}100{mu}m$ rectangulars covered with $SiO_2$film. It is shown that the etched side-wall charactistics of the pattern is vertical without dependance of the n-GaN orientations, and the smoothness of etched n-GaN surface is fairly flat.