In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined experimental results confirm the existence of a sizable induced magnetic moment at the Os site, supported by band-structure calculations, in agreement with a proposed kinetic-energy-driven mechanism of ferrimagnetism in these compounds. The intriguing property of Sr2 CrOs O6 is that it is at the end point of a metal-insulator transition due to 5d band filling and at the same time ferrimagnetism and high-spin polarization are preserved. © 2007 The American Physical Society.