A tub of a semiconductor device includes a cool zone with a first projected operating temperature and a hot zone with a second projected operating temperature greater than the first projected operating temperature. A design parameter has a first value in the cool zone and a second value different from the first value in the hot zone. The difference configures the tub to dissipate less heat in the hot zone during operation of the semiconductor device than would be dissipated if the first and second values were equal. The design parameter may be, for example, a tub width, a source structure width, a JFET region width, a channel length, a channel width, a length of a gate, a displacement of a center of the gate relative to a center of a JFET region, a dopant concentration, or a combination thereof.