This work discusses the feasibility of the series/parallel switching circuits using power MOSFETs in order to minimize the output power reduction of the photovoltaic power system due to the partial shading by connecting the shaded panels to the adjacent panel in parallel. From the experimental results: 1) When one of the photovoltaic panels is shaded at least, 50% of the reduction ratio of the solar radiation intensity becomes the lower limit of the threshold values for the series/parallel switching control. 2) The effect of the series/parallel switching control can be more expected when more than two of the photovoltaic panels are shaded. However, the sum of the solar radiation intensity applied to the panels in the parallel circuit should be less than 150% of the maximum intensity of the photovoltaic power system. 3) The shaded panel which should be connected to the adjacent panel in parallel can be detected by the bypass current measurements. The authors developed a switching circuit module prototype and carried out the operation tests using three photovoltaic panels. From the results, the switching circuit module successfully detects the partial shading conditions and switches from the series operation mode to the parallel operation mode.