Abstract: The present invention provides a field effect transistor device and a method for improving the short-channel effect and the output characteristics using the same. The field effect transistor device comprises an active layer comprising a source region, a drain region, and a channel region located between the source region and the drain region; when the device is turned on, an effective channel and an equivalent source and/or equivalent drain away from the effective channel are formed in the channel region, and the field effect transistor device connects the source region with the drain region through the effective channel, and the equivalent source and/or equivalent drain to form an operating current.