High-TcGdBa2Cu3O7−&dgr;superconductor bolometers with operation temperatures near 89 K, large receiving areas of0.95 mm2and very high detectivity have been made. The bolometers are supported by 0.62 &mgr;m thick silicon nitride membranes. A specially developed silicon-on-nitride layer was used to enable the epitaxial growth of the high-Tcsuperconductor. Using a gold black absorption layer an absorption efficiency for wavelengths between 70 and 200 &mgr;m of about 83&percent; has been established. The noise of the best devices is fully dominated by the intrinsic phonon noise of the thermal conductanceG,and not by the1/fnoise of the superconducting film. The temperature dependence of the noise and the resulting optimum bias temperature have been investigated. In the analysis the often neglected effect of electrothermal feedback has been taken into account. The minimum electrical noise equivalent power (NEP) of a bolometer with a time constant &tgr; of 95 ms is2.9 pW/Hz1/2which corresponds with an electrical detectivityD*of3.4×1010 cm Hz1/2/W.Similar bolometers with&tgr;=27 msandNEP=3.8 pW/Hz1/2were also made. No degradation of the bolometers could be observed after vibration tests, thermal cycling and half a year storage. Measurements of the noise of a Pr dopedYBa2Cu3O7−&dgr;film withTc=40 Kshow that with such films the performance of air bridge type high-Tcbolometers could be improved. ©1997 American Institute of Physics.