Thin‐film PbTe photodiodes have been operated at 80 K with significantly reduced capacitance. The technique is based upon limitation of the voltage‐induced change of the depletion‐layer volume by the presence of an insulating substrate. Capacitances as low as 64 pF for a 9‐mil‐square diode and 35 pF for a 28‐mil‐square diode have been achieved with retention of background‐limited detectivities, which were typically about 1.7×1011cm Hz1/2 W−1for peak wavelength near 5 &mgr;m.