A new high-pressure phase of FeSi with the CsCl structure has been synthesized by high-temperature reaction of Fe and Si mixtures at 24 GPa. Powder X-ray diffraction measurements yield a cubic unit cell of a = 2.7917(1) Å for the CsCl-FeSi phase which has composition Fe0.52Si0.48 by electron microprobe. The transition from ε-FeSi to the high-pressure phase occurs at 1950 ± 50 K at 24 GPa and has a negative Clapeyron slope.