The authors report on monolithic, light-emitting vertical microcavities based on an organic semiconductor single crystal. The devices are realized by reactive electron-beam deposition of dielectric mirrors and growth of tetracene crystals by physical vapor transport. The microcavities exhibit optical cavity modes in the visible range (550-580 nm) with full width at half maximum down to 2-3 nm, corresponding to a Q factor of about 200, and polarization-induced modal splitting up to 20 meV. These results open perspectives for the realization of polarized-emitting optoelectronic devices based on organic crystals.