In recent years, there have been increasing the number of power modules which is required with high performance, miniaturization and weight saving. But these requires cause high heat generation density for power module, which gets junction operation temperature to rise. Cooling unit is thus greatly demanded for high heat dissipation. The simple shaped heatsinks (straight-fin type and pin fin type) were generally used. But they have the limit of cooling performance. In this report, we have developed new heatsink shape to cope with rapidly increasing of the cooling requirement. Cooling performance is shown to thermal resistance and pressure loss. We evaluated them by thermal fluid analysis. In this approach, the spiral-fin heatsink with spiral curved channels has excellent cooling performance. This shape is the unique point in this report. This is because the shape with three-dimensional regular curve has not been studied. The spiral-fin heatsink has many factors (fin thickness, fin pitch, the number of channels, etc.). These factors affect cooler performance. We changed these factors to determine the best shape of spiral-fin. As a result, the best shape is 14.9[%] lower than the straight-fin type in thermal resistance.