Inverse semigroup equivariant $KK$-theory and $C^*$-extensions

In this note we extend the classical result by G. G. Kasparov that the Kasparov groups $KK_1(A,B)$ can be identified with the extension groups $\mbox{Ext}(A,B)$ to the inverse semigroup equivariant setting. More precisely, we show that $KK_G^1(A,B) \cong \mbox{Ext}_G(A \otimes {\cal K}_G,B \otimes {\cal K}_G)$ for every countable, $E$-continuous inverse semigroup $G$. For locally compact second countable groups $G$ this was proved by K. Thomsen, and technically this note presents an adaption of his proof.