This paper investigates experimentally the effectiveness of the vertical rectangular interrupted fins on free convection heat transfer for steady state conditions. A specially testbed designed has been developed in order to conduct a comprehensive study for heatsinks. The fin length influence, continuous fin 300 mm and interrupted fins 10, 15, 20, 25, and 30 mm with different heat flux (78,175,317,496, and 715 W) were tested on the thermal performances of the heatsink. The results of this study indicated that the thermal performance of fins has been enhanced approximately 15% by adding interrupted to heatsink, the best performance of heat transfer at fin length was ℓ = 10 mm and the so bad at ℓ = 300 mm (continuous fins). In this study can be utilized this data to improve the heat transfer by natural convection within variety applications such as electronics, communication devices and power electronics.