The clathrate‐I Ba8–xSi46 was manufactured from BaSi2 and α‐Si by high‐pressure high‐temperature synthesis at 5 GPa and 900 °C and by redox reaction from Ba4Li2Si6. The transport properties were measured on specimens from the high‐pressure high‐temperature synthesis. The composition of the Ba8–xSi46 phase [space group Pm$\bar{3}$n, a = 10.3051(1) Å] corresponds to x = 0.8(2) according to the refined lattice parameter, the value determined from full‐profile refinement of powder X‐ray diffraction data amounts to x = 0.73(1), and the chemical analysis results in x = 1.0(1), yielding the average composition Ba7.2(2)Si46. The electrical transport properties of the phase with x = 0.8 were determined in the temperature range 2–300 K using a polycrystalline bulk specimen. The material is a metallic conductor with ρ(300 K) = 3.3 μΩ m and S(300 K) = –6.8 μV K–1. The thermal conductivity shows a relatively large – for an intermetallic clathrate – value of about 8 W·K–1 m–1.