For the first time, we are proposing characteristic equation, which describes the behavior of an organic permeable base transistor (OPBT). For this, an OPBT has been fabricated and studied through the experimentally obtained ${I}_{C}$ / ${g}_{m}$ versus ${V}_{\mathsf {BE}}$ (base-emitter voltage) characteristics. The characteristic equation, i.e., collector current, ${I}_{C} = {k}$ ( ${V}_{\mathsf {BE}} - {V}_{\mathsf {th}})^{n}$ has been obtained through curve fitting and mathematical formulations. Six OPBTs (modified by inserting a layer of barrier material of either N, $\text{N}^{\prime }$ [(-di-[( $\alpha$ -naphthyl)-N, $\text{N}^{\prime }$ -diphenyl]-1, $1^{\prime }$ -biphenyl)-4, $4^{\prime }$ -diamine ( $\alpha$ -NPD) or N, $\text{N}^{\prime }$ -Bis(naphthalen-1-yl)-N, $\text{N}^{\prime }$ -bis(phenyl)-2,7-diamino-9, 9-(Spiro-NPB) between emitter and base layers) confirm that their transfer characteristics follow this equation with n varying between 1.1 and 2.2. The n has been found to be dependent on barrier material. The gain of the device is ${A}_{O} = \textit {nV}_{E}$ / ${V}_{\mathsf {BE}}$ , ${V}_{E}$ being the early voltage.