The authors propose and demonstrate a technique to determine the ion incidence angle dependence of the ion-enhanced etching yield under realistic plasma conditions and in situ in an arbitrary plasma reactor. The technique is based on measuring the etch rate as a function of position along the walls of features that initially have nearly semicircular cross sections. These initial feature shapes can be easily obtained by wet or isotropic plasma etching of holes patterned through a mask. The etch rate. as a function of distance along the feature profile provides the etching yield as a function of the ion incidence angle. The etch rates are measured by comparing digitized scanning electron micrograph cross sections of the features before and after plasma etching in gas mixtures of interest. The authors have applied this, technique to measure the ion incidence angle dependence of the Si etching yield in HBr, Cl-2, SF6, and NF3 plasmas and binary mixtures of SF6 and NF3 with O-2. Advantages and limitations of this method are also discussed. (c) 2006 American Vacuum Society.