Provided are power device substrates that comprise thermally conductive plastic materials, and power device packages including the same. An exemplary power device package includes a power device substrate that comprises a thermally conductive plastic material, and has a first principal plane that provides an electrically insulating surface and a second principal plane of which at least a portion is exposed outside a molding member. The exemplary power device package further includes one or more power devices disposed on the first principal plane of the power device substrate, and a plurality of conductive members that are electrically connected to the power device(s) in order to electrically connect the power device(s) to an external circuit.