A method to characterize the frequency response of an organic field effect transistor (FET) is presented. Analysis then shows a method to calculate the average drift mobility from the frequency at which a pole appears in the response. This pole is believed to appear at the point where charge carriers can no longer fully traverse the channel in one period of the input signal. The dc output characteristics of the device are also described, and saturation mobility values are derived. This saturation mobility and the drift mobility calculated from the frequency response are comparable. This method can be used in determining the drift mobility in other materials such as single nanowires in the FET configuration. (c) 2008 American Institute of Physics.