Provided is a field effect transistor (FET) including a gradually varying composition channel. The FET includes: a drain region; a drift region on the drain region; a channel region on the drift region; a source region on the channel region; a gate penetrating the channel region and the source region in a vertical direction; and a gate oxide surrounding the gate. The channel region has a gradually varying composition along the vertical direction such that an intensity of a polarization in the channel region gradually varies.