The extraction method of surface plasmon polariton (SPP) energy was investigated to assess its ability to improve the outcoupling efficiency of organic light-emitting diodes (OLEDs). A multi-cathode OLED (MC-OLED) structure was used; this structure was composed of a semitransparent cathode (Ag), a high refractive index dielectric layer (WO3), and a reflector (Ag). The dependence of the current efficiency of MC-OLEDs on the thicknesses of the Ag cathode and the WO3 dielectric was examined, and optimal thicknesses were identified. Current efficiency can be increased by 20% more than conventional OLEDs by using a 50-nm Ag cathode and a 100-nm WO3 dielectric.