In the present paper, we consider the regularity of the operator semigroups corresponding to the exponentially tempered asymmetric \(\alpha \) -stable processes. First, using the Fourier analysis technique, we prove that the semigroup for the tempered asymmetric stable process without drift is analytic in \(L^p(\mathbb {R})\) for any \(p\in [1,\infty )\) . Also, it is shown that the semigroup for the process with drift is an analytic semigroup if \(\alpha \in (1,2)\) , and a Gevrey semigroup of order \(\gamma \) with \(\gamma >1/\alpha \) if \(\alpha \in (0,1)\) .