Disclosed are PQFN semiconductor die packages for high-voltage, high-power applications, systems using the packages, and methods of making the packages. An exemplary package comprises a leadframe, a semiconductor die disposed on the leadframe, and a heat sink member disposed on the semiconductor die and the leadframe and integrated into the molding material of the package. The heat sink member has an electrically insulating substrate with a high breakdown voltage, and one or more conductive layers disposed on a first surface of the substrate that electrically interconnect the semiconductor to one or more leads of the leadframe.