Randy Smith, San Diego's director of player development and international scouting, said that Ruiz was one of the top players available in the international pool of players.
"We're thrilled that we were able to agree to terms with one of the premium players on the international market," Smith said.
"[Ruiz] was, in our opinion, one of the top players and the best catcher available in this year's class. He has a good frame that will fill out and add strength as he matures. [He] will be a plus receiver with an above average arm."
Ruiz, who is 6-foot-1, 180 pounds and a right-handed hitter, has a bat that has "steadily improved ... with good bat speed," Smith said. "He has a solid approach and raw power."
Saturday was the first day that international signings were permitted by Major League Baseball, which must approve the deal.