Through intracavity degenerate four‐wave interaction the reflectivity of the phase‐conjugated signal is shown to exhibit bistability and hysteresis when the driving pump field is varied in a continuous matter. The nonlinear medium inside the Fabry‐Perot cavity may be in one‐ or two‐photon resonance with the pump. We suggest suitable materials and discuss possible applications of the bistable response of the reflectivity.