We report the measured finesse value of∼390in nonabsorbingAlxOy/AlGaAscavities. The nonabsorbing cavity consisting of a bottomAlxOy/AlGaAsdistributed Bragg reflector (DBR), anAlxOyspacer layer, and a topAlxOy/AlGaAsDBR is prepared by a wet-oxidation process. The measured resonance linewidth agrees well with that of calculation, indicating very small overall losses in the cavity. The wet-oxidation process does not seem to degrade the interface of the epitaxial layers significantly. The lower bound of maximum achievable reflectivity from theAlxOyDBR is estimated to be>99.95&percent;,assuming an average interface roughness of about 0.6 nm. The maximum achievable finesse of this type of cavity is expected to be larger than that of the all-epitaxial counterpart assuming the same roughness. ©1998 American Institute of Physics.