PHOENIX, United States — Devin Booker, the high-scoring guard at the heart of Phoenix’s rebuilding plans, has signed a five-year, $158 million maximum contract with the Suns.

Booker, 21, tweeted a photo of himself smiling as he signed the contract Saturday night, moments before the Suns announced the deal, which makes him the highest-paid player in the franchise’s history.

The 13th overall pick in the 2015 draft out of Kentucky, Booker has averaged 19.8 points per game in his three NBA seasons. He averaged 24.9 points last season, shooting 38 percent from 3-point range. He won the NBA 3-point contest at All-Star weekend in February.

Booker set a franchise record by scoring 70 points in a game at Boston on March 24, 2017, just the sixth player in NBA history to score that many.

“I am humbled & honored to commit to the Suns organization long term,” he wrote. “I loved calling Phoenix home the last three seasons as this team & community are special to me. Thank you to the Suns for drafting me and believing in me. I look forward to the future & pursuing a title as a Sun.”

The announced signing came five days after Booker and his agent met with Suns owner Robert Sarver, general manager Ryan McDonough and vice president of basketball operations James Jones in Los Angeles to discuss the contract.

The contract takes effect in the 2019-20 season.

“’Book’ has been a pillar for the Suns franchise ever since he arrived in Phoenix in 2015,” McDonough said in a news release announcing the signing. “Devin and the team both wanted to extend this agreement with the club as long as we possibly could. This agreement reflects a commitment from both parties to the Phoenix community, the state of Arizona and Suns fans worldwide.”

Booker topped 4,000 career points last March 2, becoming the third-youngest player to reach that milestone. Only LeBron James and Kevin Durant were younger.

But while Booker has amassed big individual statistics, there has been little team success. The Suns have missed the playoffs the last eight seasons and had the worst record in the NBA last season at 21-61.

After the season, Booker said his days of missing the playoffs were over.

That may be a bit optimistic, but the team added to its talented core of young players big-time when it selected center Deandre Ayton with the No. 1 overall pick in the draft. Ayton and fellow first-rounder Mikal Bridges join Booker and Josh Jackson as the talented young core of the team under new coach Igor Kokoskov.

Booker will be 26, and presumably approaching his prime, when the new contract expires.