A monolithic 1.75 is mounted in a speaker cabinet 1.71 to drive the voice coil 1.74 of the speaker 1.70. The monolithic integrated circuit may be a class D amplifier 1.10, and is at least a half-bridge or full bridge power MOSFET device. Structures and process for forming the mos switching devices 2.20 of the bridge driver circuits are disclosed. Also disclosed is the N+ buried layer 4.14 of the QVDMOS transistors 4.43 of the bridge circuits.