Why did tech professionals score pay raises last year? Skill had something to do with it—but it wasn’t the only factor. Nearly a quarter of respondents to the new Dice Salary Survey said they landed a bigger paycheck through switching employers.

Although average annual pay remained relatively stagnant in 2017, at $92,712 (a mere 0.7 percent increase from 2016), the tech industry’s unemployment rate has stayed remarkably low. That’s boosted competition among employers for top talent, especially in “hot” categories such as machine learning and artificial intelligence (A.I.). Tech pros benefit from that pressure when recruiters and hiring managers dangle generous salaries as an enticement to jump to a new firm.

In the Salary Survey, some 36 percent of respondents said their most recent salary increase was due to merit; switching employers came in second, at 23 percent. In distant third: internal promotions, at 10 percent. Only 8 percent of tech pros reported a salary increase due to an employer-mandated cost-of-living bump, and even fewer—some 6 percent—said they benefitted from a generalized company-wide pay increase.

Tech pros also aren’t leveraging counteroffers, with only 1 percent reporting a salary increase because of one—the same percentage who said their pay raise was due to obtaining new certifications. Only 2 percent made more money by working overtime.

What conclusions can we draw from this data? Being really good at your job, or switching jobs altogether, are the most reliable ways to fatten your paycheck. Depending on your company for a cost-of-living increase or a “just because” raise likely won’t pay off (so to speak); and while certifications are a good way to land a new job, or ensure a bit more security in your current one, they clearly aren’t translating into salary increases for the tech pros that Dice surveyed.

With tech unemployment low, there are lots of opportunities for those tech pros with the right combination of experience and skills to jump to expanded positions at new places—and make more money in the process. The survey data also underscores what tech pros have known all along: being effective at what you do can pay off.