Kaminsky played well in the final weeks of the Charlotte Hornets' season and is expected to compete for minutes in the Suns' frontcourt.
Charlotte declined to offer Kaminsky a qualifying offer, which made the 26-year-old an unrestricted free agent.
Kaminsky was drafted ninth overall by the Hornets in 2015. He averaged 8.6 points and 3.5 rebounds per game for Charlotte during the 2018-19 season.
Kaminsky played for the University of Wisconsin, which has retired his jersey.