The highest mobility InSb epilayer grown to date by organometallic vapor phase epitaxy has been achieved by utilizing high‐purity organometallic sources, choosing a reactor geometry to reproducibly control the source concentrations above the substrate, and using a high‐ integrity reactor system. On ap‐type InSb substrate, an unintentionally doped layer had a 77 Kn‐type carrier concentration and mobility of 1.4×1015cm−3and 2.53×105cm2/V s. Growths on GaAs substrates were greatly affected by the lattice mismatch and had 77 K carrier concentrations similar to the InSb case but with mobilities of (5.0–9.0)×104cm2/V s. The crystal quality, morphology, and cyclotron resonance characteristics are reported and found to be comparable to state‐of‐the‐art molecular beam epitaxy layers.