The 49th overall pick in the 2015 Draft, Santillan pitched for Seguin High School in Arlington, Texas. He was a Perfect Game first-team All-America selection and member of the Texas All-Region first team.
A power pitcher listed between 230-240 pounds, the 18-year-old Santillan has a fastball that reaches 98 mph and a strong curveball.
Santillan is represented by agent Scott Boras.
Mark Sheldon is a reporter for MLB.com. Read his blog, Mark My Word, follow him on Twitter @m_sheldon and Facebook and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.