A Semi Flip is a quarter kickflip. Then, using the toes of your backfoot, shuv it back in a varial heelflip motion. Some people would mistakingly call it a late/underflip backfoot varial heel. While this is a good way describing the motion of the board, it is factually wrong because to execute the varial rotation of the trick, you use your toes, not your heel.
thumb|300px|left A Semi Flip is done in a few steps: First you pop a quarter kickflip (90 degree rotation). Then, using the toes of your backfoot, shuv it forwards 180 degrees, in a varial heelflip motion. It is called a semi flip because of the distinctive look of the quarter kickflip at the start.
It can be a good idea to get a regular late varial heelflip down before attempting this trick. The motions used is very similar. The distinct difference is the quarter kickflip you perform before starting the varial heel rotation. The longer the quarter flip can be suspended before starting the varial heel motion, the more distinct and exotic the actual trick looks.
Careful not to flick it to lightly, as you'll get an Impossible-esque motion with your backfoot, creating a different trick, or risking landing primo. The flick should be crisp as to get the board rotating fast enough.