MgB 2 tunnel junctions (MgB 2 /barrier/MgB 2 ) were fabricated using a native oxide grown on the bottom MgB 2 film as the tunnel barrier. Such barriers therefore survive the deposition of the second electrode at 300°C, even over junction areas of ~1 mm 2 . Studies of such junctions, and those of the type MgB 2 /native or thermal oxide/metal (Pb, Au, or Ag)show that tunnel barriers grown on MgB 2 exhibit a wide range of barrier heights and widths.a) electronic mail: Nathan.Newman@asu.edu