The low‐temperature photoresponse properties for a PbZrxTi1−xO3/YBa2Cu3O7−xthin‐film heterostructure capacitor are reported. The fast optical readout effect measured for the device while the YBCO bottom electrode was superconducting indicates a fall time dependent on YBCO state. A simple equivalent circuit model confirmed that the temperature dependence of the YBCO electrode resistance is responsible for the variation of the fall time of the optical readout signal. Such heterostructures can be used to fabricate high power, radiation‐hard optical sensors which cover the whole visible range. ©1995 American Institute of Physics.