Antibody-functionalized, Au-gated AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect c-erbB-2, which is a breast cancer marker. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 s when target c-erbB-2 antigen in a buffer at clinically relevant concentrations was added to the antibody-immobilized surface. We could detect a range of concentrations from 16.7 to 0.25 μg/ml. These results clearly demonstrate the promise of portable electronic biological sensors based on AlGaN/GaN HEMTs for breast cancer screening.