Polyacetylene/polysiloxane interface states have been investigated using metal‐insulator‐semiconductor (MIS) diodes. The 1‐mm2MIS diodes (Al/polysiloxane/polyacetylene) have been fabricated by use of a conventional photolithographic technique. TheI‐VandC‐Vmeasurements were used to explore the polyacetylene/polysiloxane interface electrical properties. The electrical conduction mechanism in this interface was found to be a Schottky‐Richardson mechanism. Using theC‐Vmeasurements to determine the interface states density distribution, it was found that the distribution had aUshape in the gap and its minimum value was 6×1013eV−1 cm−2. An attempt was made to fabricate an insulating gate field‐effect transistor which worked as a depletion‐type transistor with a very low transconductance,gm=13 n&OHgr;−1.