Espinoza, who came to the Padres from Boston last July for Drew Pomeranz, posted a 4.49 ERA in 25 Class A appearances.
Ranked 24th among all prospects by MLBPipeline.com, Espinoza isn't expected to impact the Major League club until the 2019 season. He could soon move up to the top of the organizational rankings, when center fielder Manuel Margot loses his prospect status.
AJ Cassavell covers the Padres for MLB.com. Follow him on Twitter @ajcassavell. This story was not subject to the approval of Major League Baseball or its clubs.