The new clathrate single crystal Si30.3(8)P15.7(8)Se7.930(3) was synthesized through a solid‐state reaction, and it was characterized to have a unit cell parameter a=19.7614(1) Å and belong to space group Fm
. In this clathrate structure, a Se1−Si3 bond forms in place of the tetrakaidecahedron structure, and pental dodecahedral cages composed of Si and P atoms encapsulate Se2, Se3, and Se4 guest atoms. Similar structures are observed in partial Te‐ and Ge‐substituted compounds. Theoretical calculations based on an ordered formula Si32P14Se7 showed a semiconducting electronic structure with a band gap of 0.711 eV. A photoelectric response was observed in this compound at room temperature. Across the whole temperature range, this material exhibited a weak temperature‐dependent diamagnetic signal, and no phase transition or thermal anomaly was observed in heat capacity measurements.