Two-phase thermosyphons with condensers from roll-bonded panels, short “roll-bond thermosiphons,” are attractive for power-electronics cooling. Using simulations, the performance of roll-bond thermosyphons and classical heat sinks is compared. The roll-bond thermosyphons are advantageous in terms of trade-off between thermal resistance, cooler volume or mass, and sound-power level. Under forced convection, where air-side heat-transfer coefficients are comparatively high, the classical heat sink suffers from low fin efficiency and limited heat spreading. By increasing the number of panels, the roll-bond thermosyphon enables low thermal resistances that cannot be practically reached with classical heat sinks. For free air convection, the roll-bond thermosyphon allows a significant reduction of thermal resistance and cooler mass.