AbstractA 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. ⁷⁷Se, ³¹P, and ²⁹Si 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.