An electronic method to measure the drift velocity and mobility of charge carriers in polymer thin film transistor has been developed. The measurement is based on the movement of a packet of carriers injected into the channel. This technique can be used to explore trap states and therefore obtain a comprehensive understanding of charge transport in these materials. Drift mobility of 0.52 cm2/V s is obtained from the transit time which is a factor of 3 higher than the field-effect transistor mobility.