The results of initial attempts to grow large lattice-mismatched InSb Si structures using CaF 2 buffer layers are reported. Substrate temperatures in the range of 300–400°C were used and MBE growth was initiated by opening the In and Sb shutters simultaneously, producing In-terminated InSb(1 1 1)-A surfaces on Si(1 1 1) substrates. High structural quality was confirmed by reflection high-energy electron diffraction, electron channeling and high-resolution X-ray diffraction. Electron mobility as high as 65 000 cm 2 /(V s) for a density of ∼ 2 × 10 16 cm −3 was measured at room temperature for an 8 μm-thick InSb layer grown on CaF2 Si(111).