This paper presents a detailed approach to provide improved cooling and heat spreading in electric machine rotors using centrifugally-pumped revolving thermosiphons. Design concepts are discussed that offer the following advantages: (1) high thermal performance across a wide range of operating points; (2) low-impedance heat paths; (3) excellent opportunities for integration with electric machine design for improved electromagnetic performance and structural design, as well as practical, cost-effective manufacturing. It takes advantage of centrifugal force to provide effective inertial pumping over a wide range of operating conditions. In addition, the new thermosiphon design is compatible, with existing standard electric machine manufacturing techniques and cooling needs. A condenser section fin and ramp structure provides consistently high condensation performance. Surface texture design to promote effective nucleate boiling at high speeds is discussed, and fluid fill factor is analyzed. Applications include induction and PM synchronous machines. Benefits of these thermosiphons include increased steady-state power and torque density, increased and more consistent efficiency, and reduced permanent magnet volume and cost in PM synchronous machines. Other applications may include centrifugal gas compression, chemical processes, and machine tools.