Hester, 27, has been at Triple-A Reno to start the 2011 season, batting .263 with three doubles, a home run and five RBIs in 10 games. Hester will join Triple-A Norfolk in the Orioles organization.
A 6-foot-4 Stanford product, Hester spent parts of the past two seasons in the Majors with the D-backs, batting .220 (27-for-123) with three homers and 11 RBIs in 53 games. Over two-plus seasons at Triple-A, Hester has compiled a .335 average with 15 homers and 100 RBIs. Over 300 games in the Minors, he has thrown out 29 percent of baserunners attempting to steal.
Hernandez, 25, has a 2.25 ERA through 12 appearances this season with the D-backs, allowing opponents a .205 batting average through Friday. Mickolio, 26, allowed five earned runs in five innings over four appearances with the D-backs before being optioned to Triple-A Reno, where he has posted a save in seven appearances with a 3.35 ERA.
Reynolds was batting .175 with two homers through his first 80 at-bats for the Orioles.
John Schlegel is a national reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.