Doctor Bennett was a civilian doctor working at Stargate Command in an alternate reality. He is briefly seen working on a project with the alternate Major Samantha Carter on an experiment to extract small amounts of energy from thousands of alternate realities in order to avoid the harmful effects that exotic particles could have on either of the universes connected by the matter bridge. At the precise microsecond that Major Carter was tapping into Lt. Colonel Samantha Carter's universe, Carter was out of phase, and she was transported across the matter bridge along with the entire contents of the room enclosed in her lab's force shield were transported across the bridge and into Major Carter's reality.
At that moment that Carter was being drawn in, Major Carter's equipment overloaded and exploded, killing her and Dr. Bennett and leaving no trace of them behind. Carter shifted herself back from being out of phase, only to find that she and her equipment had replaced what was there before. (SG1: "The Road Not Taken")
When Vala Mal Doran tricked Daniel Jackson into wearing a pair of Kor Mak bracelets that could not be removed, Dr. Lee advised Jackson to consider amputating his hand, as Doctor Bennett was becoming more proficient at reattaching limbs. This suggests that Doctor Bennett also exists in Lt. Colonel Carter's universe. (SG1: "Avalon, Part 1")