Patent ID: 6852559

Claim:
A method for forming a transistor of a semiconductor device, comprising the steps of: forming a stacked structure of a first epitaxial layer and a second epitaxial layer on a semiconductor substrate; forming a device isolation film of trench type defining an active region, wherein a thickness of the device isolation film is substantially the same as that of the stacked structure; implanting an impurity into the second epitaxial layer using the device isolation film as a mask; sequentially forming a thermal oxide film and a sacrificial film on the entire surface of the resulting structure; etching the sacrificial film, the thermal oxide film, and the second and first epitaxial layers using a gate electrode mask to form an opening exposing the semiconductor substrate; removing the first epitaxial layer to form an under-cut under the second epitaxial layer; forming an insulating film filling the under-cut; growing a third epitaxial layer on the semiconductor substrate exposed by the opening; removing the sacrificial film and the thermal oxide film; implanting an impurity into the third epitaxial layer to form a channel region; and forming a gate electrode on the channel region.