This paper demonstrates electrical detection of single strand deoxyribonucleic acid (ssDNA) conjugation by AlGaN/GaN hetero-structure field effect transistor (HFET) biological sensors. The probe ssDNA molecules are modified by thiol groups. The immobilization of probe molecules is achieved by S-Au bonding on a thin layer of gold film in the sensing area. The immobilization and hybridization process are firstly implemented on Si surfaces and checked by fluorescent and atomic force microscopy (AFM) imaging. The hybridization process is monitored on AlGaN/GaN HFETs. Time-dependent current change is observed when a matched ssDNA solution is applied, while no response is observed for a mismatched ssDNA sequence. The DNA hybridization process is dominated by the conjugation between matched ssDNA sequences in the first few tens of seconds. After that, the hybridization process is dominated by mass transfer processes and saturation of the immobilized probe ssDNA molecules. The paper demonstrates electrical detection of single strand deoxyribonucleic acid (ssDNA) conjugation by AlGaN / GaN hetero-structure field effect transistor (HFET) biological sensors. The probe ssDNA molecules are modified by thiol groups. The immobilization of probe molecules is achieved by S- Au immobilization and hybridization process are first implemented on Si surfaces and checked by fluorescent and atomic force microscopy (AFM) imaging. The hybridization process is monitored on AlGaN / GaN HFETs. Time the dependent hybrid change process is dominated by the conjugation between matched ssDNA sequences in the first few tens of seconds. After that, the hybridization process is dominated by mass transfer processes and saturation of the immobilized probe ssDNA molecules.