This article describes the design, manufacture, and calibration of two thermopile-type, heat flux sensors: a titanium plug sensor and a ceramic annular sensor. The intended application of both these instruments is on a high rotational speed test rig. The titanium sensor was constructed using eight thermopile junction pairs arranged in radial groves on either side of a 5-mm thickness titanium plug. The annular sensor was constructed from copper-electroplated constantan wire, wound around a 0.5-mm thickness of Macor ring. This ring was then embedded into a titanium plug. The calibrations were carried out under the stagnation point of an impinging jet onto an electrically heated surface. Existing, published Nusselt number correlations were used to provide the expected heat flux and the voltage output of the sensors was measured experimentally. The calibration for the titanium plug sensor gave an output signal significantly above that predicted by simple theory. This is consistent with an increase in the overall thermal resistance of the sensor due to the presence of the ceramic cement used to encapsulate the wires. Of the seven annular sensors calibrated, five gave similar results to that predicted by simple theory. The remaining two gave an output significantly less, which is consistent with a decrease in the overall thermal resistance, due to the presence of the copper plated onto the constantan wires.