The thermal neutron reactionn+10B→4He+7Li is utilized to measure the boron concentration on the surface of silicon wafers. This neutron depth profiling measurement technique requires no sample preparation. Boron is determined on the as‐received wafers at a level of 1012to 1013atoms/cm2. A boron level of about 2×1012atoms/cm2is found at the wafer surface after oxidation or epitaxial or polycrystalline silicon deposition. Ambient air appears to be one source of the boron. Secondary‐ion mass spectroscopy performed on wafers with polysilicon provides additional support for an atmospheric source of boron.