We show that pentacene field-effect transistors, fabricated by supersonic molecular beams, have a performance strongly depending on the precursor’s kinetic energy (KE). The major role played by KE is in achieving highly ordered and flat films. In the range KE≈3.5–6.5eV, the organic field effect transistor linear mobility increases of a factor ∼5. The highest value (1.0cm2V−1s−1) corresponds to very uniform and flat films (layer-by-layer type growth). The temperature dependence of mobility for films grown at KE>6eV recalls that of single crystals (bandlike) and shows an opposite trend for films grown at KE⩽5.5eV.