FIELD EFFECT TRANSISTOR, SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING FIELD EFFECT TRANSISTOR

摘要

PROBLEM TO BE SOLVED: To provide a field effect transistor, a semiconductor device and a method for manufacturing a field effect transistor, which can improve drain withstand voltage (BVdss-ON) in an ON state and inhibit deterioration in characteristics caused by hot carrier.SOLUTION: A field effect transistor comprises: a field oxide film 31 arranged on an N-type drift region 20 located between a channel region and N-type drain 9 of a silicon substrate 1; an N-type drift layer 21 arranged below the drift region 20 and the drain 9 of the silicon substrate 1; and an N-type field relaxation layer 25 arranged on an extension part 21A that a drift layer 21 of the silicon substrate 1 has. The field relaxation layer 25 is an impurity diffusion layer having an N-type impurity concentration higher than that of the drift layer 21.