Double sided versions of several power transistor types are devices that are already known in the literature. Devices built in this configuration are generally required to have a separate driver circuit to control the front and rear control electrodes and provide the gate or base voltage and/or currents for the power switch. This is because there may be of the order of 1000V potential-difference between the frontside and rearside potentials when the transistor is in the off condition—and a single integrated circuit cannot generally sustain this within a single package. The NPN configuration is preferred in this case to benefit from electron conduction for the main power path between the emitters. However, problems arising when using a P-type wafer. The present invention seeks to avoid the use of P-type wafers while still getting the higher conduction performance of NPN operation.