Herein, we designed several structures of GaAs/AlGaAs extended gate high electron mobility transistors (EG-HEMT) for cTnI detection, in order to explore the mechanism of bio-detection, the limit of detection (LOD) as well as the application in clinical detection. The experiment carried out that 50y structure of EG-HEMT biosensor, whose extended electrode is 50 times as large as the gate, has highest biological regulation ability (<inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula>). Meanwhile, the concentration range of cTnI detection using 50y EG-HEMT biosensor is about 100 fg ml<sup>−1</sup> to<inline-formula> <tex-math notation="LaTeX">$10~\mu \text{g}$ </tex-math></inline-formula> ml<sup>−1</sup>, which is much broader than that of Unicel Dxl800 (usually be used in clinical detection). Furthermore, due to the influence of parasitic resistance and other factors, <inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> increases with the increase of y, but the rising rate of <inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula> decreases at the same time. By comparing the detecting results of clinical samples, 30y EG-HEMT is the best in the detection of cTnI concentration with a relative error of 6%. In a higher concentration range, it is more accurate than that of the Unicel Dxl800, breaking through its limit.