A method and apparatus for switched mode power supply (SMPS) system includes circuitry configured to produce a voltage output based on an input voltage, the SMPS circuitry includes inductive, capacitive and switching elements configured to generate the voltage output. The switching elements include at least one set of cascode coupled devices, each set of cascode coupled devices including a high electron mobility transistor (HEMT) and one of a diode and a field effect transistor (FET) in a cascode coupling. A controller produces a signal to a gate terminal of the FET of the sets of cascode coupled devices to drive the HEMT switching rate to adjust the output voltage. The circuitry of the SMPS further includes circuitry to couple the substrate of at least one HEMT to a high voltage node of the SMPS system to reduce large voltage spikes or dv/dts.