The thermal boundary resistance, Rbd, at the film/substrate interface is crucially important to the thermal design of electronic and opto-electronic devices made from high-Tc superconducting thin films. Direct measurement of Rbd, however, has been limited to temperatures well above the boiling point of nitrogen, or out of the likely operating range of high-Tc devices. Here, an experiment is carried out on an Er-Ba-Cu-O thin film deposited on an MgO substrate, in which the film is etched into a double meander pattern consisting of two adjacent high-Tc strips. One strip is used as the heater, while the other is used to determine the substrate temperature. In general, the measured values of Rbd are far above those reported earlier; however, due to uncertainties in the temperature determination of the heater strip caused by its current-dependent resistance, much of the data is suspect. The most reliable data indicate that Rbd≈0.1 K cm2 W-1 at ≈100 K. Furthermore, the data suggest that Rbd may be a function of the heat flux.