The Chiefs announced that Hill's two-year contract extension will take him through to the summer of 2017.
The 20-year-old played for the Saxons in their game against Irish Wolfhounds earlier this season.
"It's great that Sam wants to stay and is prepared to commit so early," Exeter head coach Rob Baxter said.
"It's one of the signings that makes me smile when a local player who has progressed through our academy commits long-term to the club.
"The Saxons has been a great reward for him, but unfortunately he picked up a couple of injuries in that Saxons game. However, he is working really hard and will feature for us again before the end of the season."
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