Tungsten/poly(3-methylthiophene) (P3MT)/platinum diodes were fabricated by electropolymerisation of P3MT on Pt sheets and subsequent deposition of tungsten (W) by rf-sputtering. Their I-V and capacitance/conductance vs. voltage characteristics were measured at various temperatures. A novel model, taking into account the rectifying junction W/P3MT and the bulk of the polymer, was developed to analyse these characteristics. It is found that the forward-bias current is limited by the W/P3MT junction for low biases (V less than the flat-band voltage) while it becomes limited by the bulk of the polymer for higher voltages. In this bias region, space charge-limited-current with a discrete distribution of traps was dominant. In addition, the polaronic level is found to be involved in both the conduction across the junction and in the bulk of the polymer. These observations are supported by capacitance and conductance measurements.