We investigate the mobility of poly(3-hexylthiophene) (P3HT) over a carrier-density range from 1015 to 1020 cm−3. Hole-only diodes were used for densities below 1016 cm−3 and field-effect transistors were used for carrier densities higher than 1018 cm−3. To fill the gap, intermediate densities were probed using chemically doped Schottky diodes and transistors. Combining of the mobilities in doped and undoped devices experimentally establishes the full relation of the mobility over the whole carrier-density range.