Internship season is under way, and unless business students are already spending the summer with their dream employer, a full-time offer may be out of reach.

Banks and consulting firms have long funneled interns into full-time roles, but companies in other industries are increasingly turning to summer M.B.A. talent when they're ready to make permanent hires, with some locking in candidates nearly a year ahead of their start date.

At many schools, it isn't uncommon for one-third to a half of M.B.A. students to work for their summer employer after graduation, and administrators say that figure—which had dipped during the recession—is still on the rise. The trend suggests optimism on employers' parts, but it also raises the stakes for students, who begin the summer recruiting process almost as soon as they arrive on campus.

"It puts a lot of pressure on first-years to make an early decision that could affect the next three to five years," says Jack Oakes, assistant dean for career development at University of Virginia's Darden School of Business.

More than 40% of students from Darden's 2012 M.B.A. class took full-time jobs with their summer-internship employers, up from 25% in 2010. Data for the latest class aren't yet available.