An integrated semiconductor transistor chip for use in a buck converter includes a high side transistor formed on the chip and comprising a laterally diffused metal oxide semiconductor (LDMOS) transistor and a low side transistor formed on the chip and comprising a source down metal oxide semiconductor field effect transistor (MOSFET). The chip also includes a substrate of the chip for use as a source for the low side transistor and an n-doped well for isolation of the high side transistor from the source of the low side transistor.