Density functional theory calculations are performed to explain the electrical behavior of a pi-conjugated oligo(phenylene ethynylene) resembling a resonant tunneling diode. Results of this theoretical study are compatible with the assumptions that electron transport occurs through the lowest unoccupied molecular orbital, that the conduction barrier is determined by the molecule chemical potential, and that the molecule becomes charged as the external potential increases. We are able to explain the nonlinear character of the current-voltage characteristic of the molecule and its temperature dependence. The intrinsic controlled-amplification feature of these molecules is indicated.