Manufacturing jobs are increasingly going to workers with college degrees, a new analysis found.

The share of college grads in manufacturing has almost doubled since 1991.

New jobs in manufacturing often call for advanced skills such as software management and programming.

Manufacturing was once considered one of the best career options for people with only a high school degree. But a growing share of factory jobs are now going to college graduates as manufacturers upgrade their plants with robots and complex software programs.

About 40% manufacturing workers now have college degree, compared with about 2 in 10 in the early 1990s, according to an analysis from The Wall Street Journal. The shift comes at a tough time for workers with only high school degrees, with overall employment in manufacturing dropping to 9% of all U.S. jobs in 2017, from 22% in 1979.

Get Breaking News Delivered to Your Inbox Click here to view related media. click to expand

The upshot: There are now fewer good jobs in factories for workers without a college degree, Georgetown labor expert Anthony Carnevale wrote in an October blog post. It's a trend that's expected to pick up speed, with the National Association of Manufacturers noting in a study published earlier this year that "the manufacturing industry is creating more open jobs than there are skilled workers to fill them."

The manufacturing sectors with the highest share of unfilled positions are transportation equipment, chemicals, and computer and electronic products, NAM found. The group then analyzed which skills are needed in would-be employees, and discovered many fields are searching for workers with technical abilities.

For instance, transportation equipment companies are typically searching for applicants with skills such as budgeting, systems engineering and SAP software. Chemical manufacturing jobs are asking for experience with biotechnology, quality assurance and control, and chemistry, while the computer industry wants workers who can code using Python and Linux.

Robots to the rescue after nuclear disaster

Robots are part of the shift toward more educated factory workers. More companies are investing in the technology because they are cheaper than human workers, but it's also resulting in job losses. Oxford Economics estimates that robots have lead to the loss of 260,000 manufacturing jobs in the U.S. since 2000.

Those workers who remain must acquire new skills to succeed in a retooled factory. One 40-person factory near Chicago told the Journal it had overhauled its equipment since the 1990s, shifting from hand-manufactured car components to newer equipment that requires computer programming to create the parts.

"Now, it's more tech," the factory's co-owner told the publication. "There has to be more skill."