Nonpolar GaN based microcavity (MC) made of a bottom AlN/GaN distributed Bragg reflector (DBR) and a top dielectric SiO2/SiNx DBR has been fabricated on a-plane GaN template. The 13 pair AlN/GaN DBR, centered around 372 nm, exhibits a peak reflectivity of similar to 95% together with a flat stopband of 30 nm width. The cavity mode centered around 390 nm is characterized by a full width at half maximum of 4 nm. The optical properties of both the DBR and MC are well reproduced when accounting for linear birefringence effects. (c) 2008 American Institute of Physics.