The thermal‐stress fracture behavior of duplex ceramics is investigated by quenching in water and in oil. Comparison with the matrix materials shows that the critical quenching temperature difference, ΔTc, is not or is only slightly reduced, even for duplex ceramics of significantly reduced strength. In sintered composites, thermal‐stress‐induced microcracking within pressure zones and crack initiation at pressure zone–matrix interfacial defects develop before ΔTcis reached. The effects are accompanied by a gradual reduction in strength. At ΔTc, critical crack propagation occurs. The retained strength after thermal shock of duplex ceramics is significantly improved compared with the respective matrix materials. This behavior can be related reasonably well with theKR‐cu