A permutation \(\varphi \) on a group G is called a skew morphism of G if \(\varphi (1) = 1\) , and there exists an integer-valued function \(\pi : G \rightarrow Z_m\) , where m is the order of \(\varphi \) , such that \(\varphi (ab) = \varphi (a)\varphi ^{\pi (a)}(b)\) , for all \(a, b\in G\) . A skew morphism \(\varphi \) is smooth if the associated power function \(\pi \) of \(\varphi \) takes constant values on each orbit of \(\varphi \) . In this paper, we shall classify the smooth skew morphisms of semi-dihedral groups.