A GaN-based LED structure is provided so that the brightness and luminous efficiency of the GaN-based LED are enhanced effectively. The greatest difference between the GaN-based LEDs according to the invention and the prior arts lies in the addition of a masking buffer layer and a roughened contact layer on top of the masking buffer layer. The masking buffer layer contains randomly distributed clusters made of a group-IV nitride Si.sub.xN.sub.y (x,y.gtoreq.1), a group-II nitride Mg.sub.wN.sub.z (w,z.gtoreq.1), or a group-III nitride Al.sub.sIn.sub.tGa.sub.1-s-tN (0.ltoreq.s,t<1, s+t.ltoreq.1) heavily doped with at least a group-II and group-IV element such as Mg and Si. The roughened contact layer, made of Al.sub.uIn.sub.vGa.sub.1-u-vN (0.ltoreq.u,v<1, u+v.ltoreq.1), starts from the top surface of an underlying second contact layer not covered by the masking buffer layer's clusters, and then grows upward until it passes (but does not cover) the clusters of the masking buffer layer for an appropriate distance. The total internal reflection that could have been resulted from the GaN-based LEDs' higher index of refraction than that of the atmosphere could be avoided.