A field effect transistor and a semiconductor device are provided which enable a drain breakdown voltage in an off state and a drain breakdown voltage in an on state to be improved respectively. There are provided therein a field oxide film disposed on an N-type drift region positioned between a channel region of a silicon substrate and an N-type drain, an N-type drift layer disposed beneath the drift region of the silicon substrate and the drain, and an embedded layer higher in P-type impurity concentration than the silicon substrate. The embedded layer is disposed beneath the drift layer except for below at least a portion of the drain in the silicon substrate.