Presented are electronic power module assemblies with direct-cooling heat pipe systems, methods for making/using such power module assemblies, and vehicles equipped with such power module assemblies. A power module assembly includes an outer housing with an internal coolant chamber that circulates therethrough a coolant fluid. A sidewall of the module's housing defines therethrough multiple coolant windows that fluidly connect to the coolant chamber. A power semiconductor switching device is mounted to the module housing, fluidly sealed to a first coolant window with the power device's inboard surface exposed to the coolant fluid. The power device is operable to modify electric current transmitted between a power source and an electrical load. A heat pipe with an outer casing has a first casing segment thereof mounted to an outboard surface of the power device, and a second casing segment fluidly sealed to a second coolant window and exposed to the coolant fluid.