Abstract: Circuit size lower bounds were previously established for functions in NP(NP), ZPP(NP), NEXP(NP), ZEXP(NP), and MAEXP. We ask the general question: Given a time bound t(n). What is the best circuit size lower bound that can be currently shown for the classes MATIME[t(n)], ZPTIME[t(n)], ... ? For the classes MAEXP, ZEXP(NP) and NEXP(NP), the answer turns out to be "half-exponential". Informally, a function f is said to be half-exponential when f(f) is exponential. Such functions were constructed by Szekeres.