K₂SiH₆, crystallizing in the cubic K₂PtCl₆ structure type (Fm3̅m), features unusual hypervalent SiH₆^2– complexes. Here, the formation of K₂SiH₆ at high pressures is revisited by in situ synchrotron diffraction experiments, considering KSiH₃ as a precursor. At the investigated pressures, 8 and 13 GPa, K₂SiH₆ adopts the trigonal (NH₄)₂SiF₆ structure type (P3̅m1) upon formation. The trigonal polymorph is stable up to 725 °C at 13 GPa. At room temperature, the transition into an ambient pressure recoverable cubic form occurs below 6.7 GPa. Theory suggests the existence of an additional, hexagonal, variant in the pressure interval 3–5 GPa. According to density functional theory band structure calculations, K₂SiH₆ is a semiconductor with a band gap around 2 eV. Nonbonding H-dominated states are situated below and Si–H anti-bonding states are located above the Fermi level. Enthalpically feasible and dynamically stable metallic variants of K₂SiH₆ may be obtained when substituting Si partially by Al or P, thus inducing p- and n-type metallicity, respectively. Yet, electron–phonon coupling appears weak, and calculated superconducting transition temperatures are <1 K.