Band structure of III-V material InSb thin films is calculated using empirical pseudopotential method (EPM). Contrary to the predictions by simple effective mass methods, our calculation predicts that the Γ valley (with the smallest isotropic bulk effective mass) in InSb remains the lowest lying conduction valley despite size quantization effects in the presence of competing L and Δ valleys which have larger quantization mass. Based on EPM, we computed the important electronic parameters (effective mass, valley minima) of InSb thin film as a function of film thicknesses. Our calculations reveal that the 'effective mass ' of Γ valley electrons increases with the scaling down of film thickness. We then studied the transport of InSb thin film using Non-Equilibrium Green's Function. The calculation reveals that InSb is comparable but not superior to Si as channel material of ultra-thin body double gate n-MOSFET in the ballistic limit of these devices.