Photovoltaic/thermal (PV/T) systems generally use the crystalline silicon (c-Si) solar cells, and the electrical efficiency will decline as the temperature of PV modules increase. Study on the PV/T using amorphous silicon (a-Si) cells is rare. The a-Si cells may perform better at higher operating temperature regarding the effect of thermal annealing. They are able to exhibit positive power temperature coefficients at degraded steady-state(DSS). Unlike c-Si cells-based PV/T collectors suffering from poor thermal conductivity and large thermal stress due to the fluctuation in operating temperature, a-Si PV/T collectors are made of thin and flexible cells that can be easily deposited on metal (e.g. stainless steel), and are thus promising in the medium/high temperature applications. A novel a-Si cell based PV/T system is designed, constructed and tested in this paper. Two modules of the PV/T collectors are investigated. The outdoor performance of the a-Si PV/T collectors is analyzed. The a-Si cells’ operating temperature, maximum power point current and voltage, inlet and outlet temperature of collectors, water-storage tank temperature together with solar irradiation, water mass flow rate, ambient temperature have been measured. The thermal efficiency, electrical efficiency with maximum power point tracking (MPPT) and the I-V characteristic are examined. The results show that the maximum instantaneous thermal efficiency of the system can achieve 42.49% with the maximum instantaneous electrical efficiency of 5.62%. The daily thermal and electrical efficiencies are 28.7% and 5.32%, respectively, and the overall efficiency of the a-Si PV/T system is 39.25%. The technical feasibility of the a-Si PV/T can be preliminarily demonstrated by the prototype.