The effects of fairly high densities of extrinsic stacking faults (&agr; approximately as large as 0.3) and twins (&bgr; approximately as large as 0.15) on the coercive force,Hc, of thin (less than 700 Å) ferromagnetic Fe‐Co‐Ni films are studied.Once the effects of strain and small crystallite size onHcare eliminated, it can be shown that stacking faults and twins increase theHc, stacking faults having a larger effect than the twins. The introduction of the faults was achieved by sputtering onto ``unclean'' substrates, which gave an initial small‐crystallite‐size layer of about 100 Å, where the crystallite size gradually increased to that found on ``clean'' substrates. At the intersection of the two layers, there was a layer of faults extending about 200 Å into the larger‐crystallite‐size film. The x‐ray technique used to evaluate thickness variation of faults is described.