Johnson, 26, averaged 13.7 points, 5.4 rebounds, and 1.4 assists this season with San Antonio while shooting a stellar 52%, joining Spurs legend Manu Ginobili (2007-2008) as the only two ever to win the award in franchise history.
The seven-year veteran who played all 82 games put up 1,081 bench points, surpassing Ginobili's 927 when he won the award.
Johnson took home 63 first-place votes over Miami Heat's Jaime Jaquez Jr. and the Denver Nuggets' Tim Hardaway Jr.
Jaquez Jr. finished with 34 first-place votes, while Hardaway Jr. didn't receive any, still finishing third in total points from seven second-place votes and 24 third-place votes.
This is Johnson's first award since being selected with the 29th overall pick in the 2019 NBA Draft by the Spurs. He currently has one more year left on his deal and is set to make $17.5 million next season.
