An approach is proposed for the realization of a vertical-cavity surface-emitting semiconductor micro-optical parametric oscillator that relies on the use of third-order excitonic nonlinearity in isotropic semiconductors. We demonstrate that a planar triple microcavity structure can be designed to provide triple resonance for the parametric frequencies together with built-in cavity phase-matching for all waves at normal incidence. An example is given of a monolithic structure consisting of three strongly coupled AlGaAs/GaAs lambda microcavities including single InGaAs quantum wells. Applications to the generation of twin photons or entangled photon pairs are discussed.
