The 21-year-old scored 718 Championship runs this year - at an average of 31.22 - and also helped Somerset win the One-Day Cup title at Lord's.

Academy graduate Bartlett only signed his previous deal in January.

"I'm really looking forward to the next three seasons with this squad because the club is in a really exciting place at the moment," he said.

Somerset director of cricket Andy Hurry told the club website: "We look forward to helping George fulfil his potential and move closer to winning international recognition over the next few years."