Java developers remain the most difficult vacancies to fill, say US employers. This is followed by mobile developers, .NET developers and software developers, according to a recent survey.

Hiring managers and recruiters cite these positions up to three times more frequently than other skill sets in the employment marketplace, according to a study conducted by in the US.

The IT jobs site polled 866 tech-focused hiring managers and recruiters to come up with its list of hard-to-fill positions. Rounding out the top 10 list are candidates with skills related to: security, SAP, SharePoint, web development, active federal security clearance, and network engineering.

In general, companies are looking for candidates with at least a few years of experience.

Asked for experience preference, corporate hiring managers most frequently say IT pros with two to five years in the workforce, followed by those with six to 10 years of experience, the Dice research found.

"Competition is fierce when companies are all chasing the same talent, making positions hard to fill," said a company spokeswoman.

Companies are less focused on internal talent development than they have been in the past, and formal corporate IT training opportunities aren't widespread. This has sharpened competition for talent.

"Companies have been shifting the responsibility for training their employees to the individual for decades. Hiring managers say they expect tech professionals to stay with their firm about three years. That makes it tough to cross-train, retrain, or train at all," said the spokeswoman.