On a p-type silicon wafer with n(+) source and drain contacts, covered by a SiO2/Si3N4 dielectric insulating layer, field-effect transistors were made by spin coating with a polyaniline gate electrode layer. For comparison conventional IGFETs were also made on the same chip. Preparation and characterization of devices that change their threshold voltage due to modulation of work function of the gate electrode are described. Such devices can in principle be used for gas sensing. The steady-state and transient behavior of the devices was investigated : the work function of polyaniline has been determined by comparing the metal-oxide-semiconductor field-effect transistor threshold voltage to the polyaniline gate field effect transistor (PANi-FET) threshold voltage. The response of the PANi-FETs to a step function potential input has been determined. The device behavior was modeled with a simulation in which the gate and pre-gate area are represented by a distributed resistance capacitance network, under the assumption that the resistivity of the polyaniline film and ifs contact resistance to platinum is not frequency dependent. The behavior is well described by the model.