Abstract: In the quantities analysis of trace impurity boron in heavily As doped silicon crystal using second ion mass spectrometry (SIMS), it is occasionally observed that the boron concentration level in some local regions at the surface is tremendous higher ( as high as 10-16 atom/cm³ ) than the normal level. If the analysis region is shifted few hundred microns, however, the boron concentration level reduces to normal level (＜1×10¹⁴atom/cm³) at once. Based on heavily As doped silicon crystal manufacturing process, boron distribution in the silicon crystal should be uniform. Furthermore, n/n⁺ epitaxy silicon wafers manufactured by such kind of silicon crystal exhibits good quality with the specifications. It was estimated that the abnormal distribution phenomena of boron concentration in the heavily As doped silicon during the SIMS analysis should be induced possibly by the oxygen existing in the silicon crystal.