Five days after acquiring outfielder Scott Hairston from San Diego, Oakland has made another deal before the All-Star break, this time adding to their farm system's pitching depth by acquiring the right-hander Souza.
Hannahan, a 29-year-old left-handed hitting third baseman, was optioned to Triple-A Sacramento on June 29 after hitting .193 with one home run and eight RBI in 119 at-bats for the A's this season.
Hannahan played in 108 games at third base for the A's last season, filling in for the injured Eric Chavez, and became known as one of the better defensive players at the position in the American League. However, he struggled offensively, finishing last in the Majors with a .218 BA.
"He gave us everything he had, played hard, good teammate and he'll get a chance to go back to the Major Leagues so I'm happy for him in that respect," A's manager Bob Geren said. "He's very professional on and off the field."
Souza was Seattle's ninth-round pick in the 2006 First-Year Player Draft. He split the 2008 season with Class A Wisconsin, High Desert and Triple-A Tacoma, compiling a 3.90 ERA.
"He's doing well, he has a nice ERA, strikeouts-to-walk ratio," Geren said of Souza. "Pretty impressive what he's done."
Zach Schonbrun is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.