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We report on epitaxial crystal growth and spin Hall effect in BiSb topological insulator thin films. We show that BiSb thin films with conductivity as high as σ ~ 2.5∗105 Ω-1m-1 can be epitaxially grown on GaAs(111)A substrate. Meanwhile, evaluation of spin-orbit-torque in Bi0.9Sb0.1/MnGa bi-layers reveals a colossal spin Hall angle of θSH ~ 52 and a spin Hall conductivity σSH ~ 1.3∗107 ℏ/2e Ω-1m-1 at room temperature. We demonstrate that BiSb thin films can generate a colossal spin-orbit field of 2.3 kOe/(MA/cm2) and a critical switching current density as low as 1.5 MA/cm2 in Bi0.9Sb0.1/MnGa bi-layers. BiSb is the best candidate for the first industrial application of topological insulators.