AlAs‐GaAs‐AlAs double‐barrier resonant tunneling diodes (DBRTDs) with different doping levels in the AlAs layers have been investigated. Two‐step spacer layers were used in all samples. Peak‐to‐valley current ratios (PVCRs) as high as 3.5 (11.3), 3.5 (11.3), and 2.7 (8.2) were observed at 300 K (77 K) for samples with undoped, 1.2×1017cm−3, and 3×1018cm−3doped AlAs barriers, respectively. These results indicate that resonant tunneling is not strongly affected by ionized Si atoms in the AlAs barriers. The excellent PVCRs observed in DBRTDs with two‐step spacer layers is not because of low background impurity densities in the active region, but because of a third barrier formed by band bending in the spacer layers.