FinFETs may in principle be built on either bulk [1–3] or SOI [4–5] substrates. In this paper we will review some of the technical issues associated with choice of substrate, directly comparing empirical results on 10nm hardware for which all the other processes are as much the same as possible. Furthermore, we will discuss the challenges beyond the 10nm generation, where fundamental changes in materials may render the debate moot. Our conclusion and prognosis is that SOI was, is, and will continue to be the technically superior choice.