We demonstrate doping-tunable mid-infrared extraordinary transmission through periodic sub-wavelength openings in thin metal films. This effect, known as extraordinary optical transmission, is thought to result from the excitation of Surface Plasmon Polaritons at the metal/dielectric interface. The metal aperture arrays studied were fabricated upon GaAs substrates. Because the dielectric constant of a semiconductor changes with carrier concentration, identical metallic grating show different spectral characteristics as a function of GaAs epilayer doping. Thus, the resonant transmission peaks of our grating structures can be shifted by varying the doping of the n-GaAs epilayer upon which they are fabricated. We demonstrate peak shifts of 37 cm-1, or approximately 0.33 urn, as we move from undoped GaAs layer to highly doped n-GaAs layers. Additionally, we study the effect of doping layer thickness on the resonant transmission peak position, which allows for an estimate of the surface plasmon strength as a function of distance from the metal/dielectric interface. Furthermore, we present calculated results for our samples and compare them to our experimental results and propose an explanation for the slight discrepancy between theoretical and experimental results. The devices presented could eventually lead to voltage-tunable mid-IR mirrors, filters, or modulators.