Abstract. Let S be a finite semigroup and let A be a finite dimensional S-graded algebra. We investigate the exponential rate of growth of the sequence of graded codimensions c S n (A) of A, i.e lim n→∞ n c S n (A). For group gradings this is always an integer. Recently in [20] the first example of an algebra with a non-integer growth rate was found. We present a large class of algebras for which we prove that their growth rate can be equal to arbitrarily large non-integers. An explicit formula is given. Surprisingly, this class consists of an infinite family of algebras simple as an S-graded algebra. This is in strong contrast to the group graded case for which the growth rate of such algebras always equals dim(A). In light of the previous, we also handle the problem of classification of all S-graded simple algebras, which is of independent interest. We achieve this goal for an important class of semigroups that is crucial for a solution of the general problem.