Data are presented characterizing the spontaneous coupling to both planar and index‐confined quasimodes of Fabry–Pe´rot microcavities. Index confinement is achieved using selective conversion of AlAs–AlxOythrough ‘‘wet’’ oxidation to fabricate lateral cavity sizes as small as 2 &mgr;m diam. Spectral tuning and angular radiation patterns show the increased spontaneous coupling that results from three‐dimensional confinement. ©1995 American Institute of Physics.