AlGaN/GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The gate area was deposited with Au and thioglycolic acid. The antibody was anchored on the gate area. The AlGaN/GaN HEMT drain-source current showed a rapid response of less than 5 seconds when the target toxin in a buffer was added to the antibody-immobilized surface. Different concentrations (from 0.1 ng/ml to 100 ng/ml) of the exposed target botulinum toxin in a buffer solution were detected. The sensor showed low detection limit of less than 1ng/ml and saturates above 10ng/ml of the toxin. The sensor was recycled with the phosphate buffered saline (PBS) after the toxin detection and still showed the same sensitivity.