Bostrom raced for Kawasaki from 1999 to 2003 riding the ZX-7R in the AMA Superbike Championship. He also rode the ZX-6R in the AMA Supersport Championship, winning the AMA Supersport championship in 2001. In 2001, Bostrom finished second in the AMA Superbike Championship to Mat Mladin. He also finished second in the AMA Superbike Championship in 2002, this time behind Nicky Hayden. During his career at Kawasaki, Bostrom was able to compete in several World Superbike events. This, coupled with his back-to-back second-place finishes in AMA's highest class lead many observers to believe a transfer to World Superbike, or possibly MotoGP was in Bostrom's future. Injuries marred his 2003 season and Kawasaki pulled out of AMA competitions.