An experimental and analytical study was conducted to evaluate a planar heat pipe used as a cooling fin for high density heat dissipation. Both natural and forced convection configurations were investigated. For forced convection, the thermal resistance of the heat pipe, 100 mm x 90 mm x 5 mm in dimensions, was more than three times smaller than that for a solid fin with the same dimensions when the heat dissipation rate exceeded 10 W cm(-2) and the heating temperature was under 100 degrees C. The improved performance makes planar heat pipes viable alternatives to conventional solid fins, for applications requiring efficient and reliable heat dissipation.