This study reports a fluorescence detection system using bio-sensors, combining AlGaAs/GaAs photo-transistors with a biomarking technique for sensing human serum albumin (HSA). Following excitation, the fluorescence of biomarkers was used as the signal source and an AlGaAs/GaAs heterojunction photo-transistor with micro-flow channels and built-in amplification was used as the sensing device. The entire chip comprised a total of 808 connected photo-transistors and a total sensing area of 18.18 mm2. Linear results were observed in the sensing range of 0.01 to 0.07 mg/mL with the sensing current of 1.75 to 2.62 μA, which covers the range from normal to slight proteinuria required for early warning applications. In addition, the HSA bio-sensor can be reused promptly after flushing the device with pure water.