Along with photovoltaic systems which produce electrical energy from solar radiation, a photovoltaic/thermal system simultaneously produce electricity and heat. In this research, a photovoltaic/thermal system was designed using a series of thermosyphons (gravity assisted heat pipes) to cool the photovoltaic panel. Because of high vapour pressure, methanol was used as the working fluid in the thermosyphons. During the experiments, the filling ratio as one of the most important parameters affecting the thermosyphon performance , varied at different values. At the optimal filling ratio e.g. 50%, 5.67 percent more electrical power in average was produced from the photovoltaic/thermal system compared to the photovoltaic one. Additionally, the photovoltaic/thermal system had 16.35 percent thermal efficiency in average.