<p>Boiling heat transfer (BHT) is a promising technology for next-generation electronics cooling because it provides a high heat-transfer coefficient, typically more than an order of magnitude larger than that of single-phase liquid convection. However, practical implementation of BHT in electronics cooling faces critical challenges, particularly accurate identification of the onset of nucleate boiling (ONB) and the critical heat flux (CHF). Therefore, experimental studies are essential to elucidate the mechanisms of ONB and CHF. A major difficulty in such experiments is obtaining reliable boiling curves that characterize BHT under various conditions. In particular, measurement uncertainties in the heat flux and heat-transfer surface temperature can be significant. In this study, we investigate the impact of thermocouple positioning errors in a heating block by incorporating the hot-junction locations in sheathed thermocouples identified using X-ray micro-computed tomography (µCT). We evaluate the uncertainty using a conventional method and compare it with that assessed by numerical heat-conduction analysis based on a µCT-reconstructed 3D geometry. The results suggest that the hot-junction position and thermocouple insertion conditions are key factors in reducing measurement uncertainty in BHT experiments.</p>