Enhancement of the resonant peak current through the ground quantum-well state at room temperature is observed at a low voltage by adding the second quantum-well structure to the AlAs/GaAs (001) double-barrier single quantum-well heterostructure. The peak to valley current ratio increases slightly with the increasing temperature up to room temperature, and shows stable characteristics up to high temperature in this AlAs/GaAs (001) triple barrier heterostructure. The results indicate that the optimum alignment of the Fermi level with the lined-up quantum-well states can greatly improve the resonant peak current in the low voltage range, and therefore device characteristics. ©1997 American Institute of Physics.