The reversal process of the Fe interface layer magnetization in Fe/AlGaAs heterostructures is measured directly using magnetization-induced second-harmonic generation, and is compared with the reversal of the bulk magnetization as obtained from magneto-optic Kerr effect. The switching characteristics are distinctly different due to interface-derived anisotropy—single step switching occurs at the interface layer, while two-jump switching occurs in the bulk Fe for the magnetic field orientations employed. The angle between the interface and bulk magnetization may be as large as 40–85 degrees. Such interface switching will dominate the behavior of nanoscale structures.