KLiSiF6 and CsLiSiF6 were synthesized via a high‐pressure/high‐temperature synthesis route. Even though, both substances crystallize in the orthorhombic crystal system with space group Pbcn (no. 60), they show different crystal structures. Main motifs of KLiSiF6 are an [SiF6]2- and an [LiF6]5- unit. In contrast, the main motifs of CsLiSiF6 are an [SiF6]2- and an [LiF5]4- entity. Within both substances, these units are interconnected and form 3‐dimensional networks. The substances were characterized via single‐crystal and powder X‐ray diffraction, as well as infrared spectroscopy and EDX measurements. Additionally, Mn4+‐doped KLiSiF6 was analyzed by means of luminescence spectroscopy. It displays line emission in the red spectral region. The maximum emission wavelength is λ[lambda]max=631 nm.