The effect of intrinsic gettering on the minority-carrier generation lifetime (tau(g)) of Si MOS devices fabricated on CZ and HMCZ Si substrates of varying interstitial oxygen concentration was investigated. Wafers cut from 57 mm diameter Si ingots grown under a horizontal magnetic field of B = 0 to B = 5.4 kG were divided into three groups according to the initial interstitial oxygen concentration: low oxygen (8-12 ppma (New ASTM)), medium oxygen (13-17 ppma), and high oxygen (18-20 ppma). When subjected to an intrinsic gettering method consisting of 1150 degrees C/1 h denudation and 650 degrees C/1 h nucleation preanneal followed by 1000 degrees C/11 h process simulation anneal, the medium-oxygen CZ Si specimens by far showed the best intrinsic gettering effect, yielding a generation lifetime (tau(g)) of 26.7 mu s as compared to those of 5 mu s or less observed in other specimens. Apparently, the low-oxygen CZ Si specimens lacked sufficient SiOx nuclei to cause oxygen precipitation required for intrinsic gettering, while the high-oxygen CZ Si specimens had too many SiOx nuclei to cause the oxygen precipitation terminate prematurely during the 1000 degrees C/11 h process simulation step. As for the HMCZ Si specimens, on the other hand, the lack of grown-in defects, which may work well for nongettering processes, is believed to have muted the effect of the intrinsic gettering heat treatment.