Depends on what you are hunting. Semi automatic is just a repeating rifle, one that auto reloads the next round after a shot. You still have to release the trigger and pull the trigger again to get that round to fire. One round per trigger pull, but the next round auto loads. Remington makes semi automatic shotguns.
An AR 15 is a great varmint gun, but most are a little small on caliber and accuracy for hunting large animals. Maybe rabbits and such. They have a bad rap in general because they look like automatic weapons (which imo no one actually needs outside of war or a stampede coming at you), but a Winchester 308 is far more accurate and deadly. The bad thing about an ar15 is that it can be broken down and hidden easier and that, again imo, is a reason you hear about them in shootings. Someone would notice a person carrying a 308. An AR 15 will fit in a backpack.