Implementations of high-power semiconductor device modules are described, including automotive power transistor assemblies for use in power amplifier circuits such as a cascode circuit. In some implementations, power amplifier circuit components are provided on separate semiconductor die attached to discrete dual die attach pads. A separation between the die attach pads, as well as a through-hole, provide sufficient isolation between the die to permit operation of the circuit at high voltages without relying on a thick multi-layer direct bond copper (DBC) isolation structure. In some implementations, higher voltage operation can be supported by a thin multi-layer, resin coated copper DAP in which the top layer is split.