The peak current for the negative differential resistance region of AlGaAs/GaAs resonant tunneling diodes is shown to behave independently of the width of a low-doped emitter spacer layer if an isolated accumulation region forms upstream from the first AlGaAs barrier. The effect of the voltage drop across the emitter spacer layer is shown to be minor. These results appear to confirm that electron transport through these resonant tunneling diodes is a two-step process. In addition, a radial dependency of device performance attributed to molecular beam epitaxy growth conditions is noted.