Schottky barrier heights are measured by current‐voltage and capacitance‐voltage methods for Al/n‐GaAs contacts with a rare‐earth metal (Sm, Dy, Yb) interlayer, which forms a stable alloy with Al but does not form an electrically active site in GaAs. The Schottky barrier height for each contact is found to be lowered with diode factorn<1.06, compared to ideal Al/n‐GaAs and rare‐earth metal/n‐GaAs contacts. The mechanisms for the lowering are discussed from standpoints of alloy formation and diffusion across the interface.