A luminescent EuIII coordination polymer with O2‐sensing units under air, EuIII‐hcpt (hcpt: 2,3,6,7,10,11‐hexakis(4‐carboxy‐phenyl)triphenylene), is reported. The hexadentate carboxylic acids in hcpt ligands play an important role in the formation of tight‐packed three‐dimensional networks in EuIII‐hcpt, giving hyper thermo‐stable structures (decomposition temperature=420 °C). The three‐dimensional porous network promotes bright luminescence (4f–4f emission quantum yield=70 %). The emission lifetime of EuIII‐hcpt under vacuum (0.86 ms) was twice as large as that under O2 (0.48 ms, 1 atom:101.3 kPa). The Arrhenius analysis of the emission decay profile indicates that the back energy transfer (BEnT) from the emitting level of the europium(III) ion to the excited T1 state of the hcpt ligand should be activated at room temperature. The gradual decrease of emission lifetime is caused by the BEnT process in EuIII‐hcpt. Finally, an advanced pressure‐sensitive luminophore is demonstrated.