Adhesion strength evaluation of molding compounds is a critical issue in structural design and material selection for IC plastic packages. However, since conventional adhesion tests can only give apparent adhesion strengths, which include the effect of residual stress, their results cannot be used for design purposes. This paper proposes a new strength evaluation method which can experimentally separate residual stress from adhesion strength. In this method, three-point bending tests of ENF specimens are performed in both directions. Residual stress is then cancelled by simply averaging the apparent strengths for both directions. The method’s validity is verified by experiments and stress analyses of specimens composed of an IC molding compound and Alloy 42 lead frame material. Adhesion strength is expressed in terms of the stress intensity factor of the interface crack. It is confirmed that constant strengths can be obtained independently of specimen dimensions.