Iron is one of the most important impurities in silicon integrated‐circuit technology. We present a fast (5 min), essentially preparation‐free large‐area (25 cm2) technique to determine the Fe concentration in boron‐doped silicon with a sensitivity of 2–5×1011cm−3. The principle of the method is based on the fact that interstitially dissolved Fe undergoes a reversible pairing reaction with boron and that the minority‐carrier diffusion length—as measured by the surface photovoltage method—is modified by this reaction. The method has been calibrated by deep‐level transient spectroscopy and is also suitable to measure a surface Fe contamination in combination with a rapid thermal annealing diffusion step.