Abstract  To reliably immobilize different biomoieties on surfaces of III-V semiconductors is one of the most critical issues in the development of biodetector devices based on the optical/electronic properties of these materials. Herein we demonstrate the successful immobilization of avidin, a robust and well-studied protein, on a (001) GaAs surface. The immobilization was investigated via specific binding to biotin, which was connected to the GaAs surface through commercially available long- or short-chain amino group terminated alkanethiols (HS(CH₂)₁₁NH₂ or HS(CH₂)₂NH₂), or through a biotinylated thiol synthesized in our laboratory. The immobilization performance was evaluated by photoluminescence and fluorescence microscopy measurements. We found that the biotinylated thiol mixed with a diluent thiol provides the highest avidin immobilization efficiency.