A new heterocyclic four-membered CPSeSi cation was synthesized in its racemic form by B(C6F5)(3)-mediated ring-closing reaction starting from the hydrosilane precursor. The cation has an asymmetrically substituted silicon center, which is stabilized by a selenium-silicon bond. The phosphonium hydroborate and its precursor were characterized by single-crystal X-ray diffraction analysis and NMR spectroscopy. Se-77, P-31, and Si-29 NMR spectroscopic parameters proved to be sensitive probes for determining small electronic changes around the silylium-type center. Density functional theory (DFT) calculations of the ring-opening energy of the selenium-based cation gave insight into the stability of the Se-Si bond and revealed a stronger intramolecular stabilization of the silicon atom compared to a coordinating phosphane sulfide function. For the first time, the influence of a C6F5 group at the silicon atom of these type of cations was also investigated, showing a slightly increased stabilization of the Se-Si linkage in the cyclic selenium-based cation.