A novel two-phase thermosyphon based on automotive technology is presented as a valid solution for the cooling of power-electronic semiconductor modules. A horizontal evaporator configuration is investigated. This solution is based on a 90 deg-shaped thermosyphon that allows an optimal geometrical arrangement of the cooler with limited volume occupancy, reduced air pressure drop, and weight as well as optimal thermal performance compared with standard heat-sink technology. The 90 deg-shape refers to the mutual arrangement of the evaporator body and the condenser, which are in a horizontal and vertical position, respectively. The evaporator cools three power modules with a total power loss between 500 and 1500 W. Experimental results are presented for inlet air temperatures ranging from 20 to 50 °C and for different air volume flow rates between 200 and 400 m3/h. The working fluid is refrigerant R245fa. The maximum thermal resistance (cooler base to air) attained values between 40 and 50 K/kW.