Assuring the process capability in nonlinear profiles to meet the requirement is a very important task. This paper aims at evaluating the process yield for nonlinear profiles in manufacturing processes. We present the statistical properties of the estimated SpkA and obtain its lower confidence bound. This index provides an exact measure of the process yield for nonlinear profiles. A simulation study is conducted to assess the performance of the proposed method. The simulation results confirm that the estimated SpkA value is close to the target value and has the smallest standard deviation. One real example is used to demonstrate the application of the proposed approach. Copyright © 2013 John Wiley & Sons, Ltd.