Ross was 2-11 with a 6.50 ERA in 18 games (13 starts) for the A's and went 6-2 with a 2.99 ERA in 15 games (13 starts) for Triple-A Sacramento.
The 25-year-old was originally selected in the second round of the 2008 First-Year Player Draft and had appeared in 53 games for the A's over the past three seasons. He is a hard thrower who also possesses a plus slider.
Ross' brother, Joe, was the Padres' first-round selection in the 2011 Draft.
Building up their inventory of pitching is a priority for the Padres after they used 15 starters last year following injuries to Dustin Moseley, Tim Stauffer, Cory Luebke and Joe Wieland.
Luebke and Wieland each had Tommy John surgery and won't return until mid-2013 at the earliest.
The Padres are exploring all avenues to acquire pitching and have been linked to free agent Dan Haren, who pitched for Padres general manager Josh Byrnes when Byrnes was GM of the D-backs.
Kirby-Jones spent last year with Class A Stockton, where he hit .248 with 16 doubles, three triples, 21 homers and 69 RBIs in 115 games. A prospect with some pop, Kirby-Jones had a .382 on-base percentage and slugged .461 for Stockton.
The 24-year-old was originally drafted in the ninth round of the 2010 First-Year Player Draft and primarily played first base last season.