Interfacial reactions between contacts and semiconductors have been studied for years because of the close connection between these reactions and the electrical characteristics of the contacts. These reactions furthermore control the thermal and morphological stability of the contacts, and many features of the reactions can be predicted and controlled if thermodynamic and kinetic considerations are used to design contact metallizations. Such an understanding of the metallurgy of contacts to GaN has begun to emerge in recent years. For the group 111 nitride semiconductor alloys, such as AIx,Ga1-x,N, most contacts that have been employed are very similar to those for GaN. However, there are additional phenomena that occur in contacts to alloy semiconductors that do not occur in contacts to other semiconductors. In fact, a few researchers have already taken advantage of polarization effects in graded alloy layers and at heterointerfaces to engineer the performance of contacts using group 111 nitride semiconductor alloys. In this presentation, we explore a special consideration of the contact metallurgy for alloy semiconductors that has received little attention to date-how interfacial reactions with metals can lead to compositional shifts in the semiconductor alloys beneath the contacts.