In this paper, we establish the existence of transition density for geometric $α$-stable processes by using the property of self-decomposability--a fundamental concept in the theory of Lévy processes. In contrast to traditional and analytic methods that often rely on the $L^{1}$-integrability of the characteristic function, our approach is purely probabilistic and focuses on the structural regularity of the Lévy measure. As an application, we prove the existence of ground states for Schrödinger operators associated with recurrent geometric stable processes.