Hernandez was 7-2 with a 2.90 ERA in 14 appearances, including 13 starts, in the minors this season. He was named this season to the Double-A Southern League All-Star team and was promoted to Triple-A on July 6 and had a 3.75 ERA in two starts there. He was acquired by the White Sox as part of the Carlos Quentin trade with the San Diego Padres in 2011.
Hernandez replaces Jhan Marinez, who was optioned on Tuesday.
Hernandez is the 12th rookie and 10th pitcher to appear on the White Sox’s 25-man roster this season.