The median income for all Americans was $35,540 in 2013, up slightly from the year before. At a number of U.S. companies, salaries are considerably higher. Based on figures provided by Glassdoor, 24/7 Wall St. examined the 15 highest paying companies in America. At these companies, the median annual compensation is at least four times the nationwide median income.

The companies that pay their employees the most fall primarily into two industries: consulting firms and tech companies. These companies attract some of the nation’s most highly-skilled workers, who demand high salaries to match their expected performance.

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According to Andrew Chamberlain, chief economist at Glassdoor, both types of high-paying companies require very high-skilled workers. However, these workers are highly paid for very different reasons.

Six of the highest paying companies are consulting firms, law firms, accounting firms, or some combination of the three. Chamberlain explained there are barriers to competition in these kinds of companies. It is very difficult to uproot very old firms with relationships cultivated over long periods of time by very experienced employees.

“When you are a consulting firm you don’t have much in the way of machines and other capital,” Chamberlain said. Instead, “you have a little bit of software, you have an office space, but your main asset is the human capital in the heads of your partners.” The value of these types of companies is disproportionately in their employees, and they are highly paid as a result.

The other nine companies are in the information technology sector, particularly semiconductor manufacturing and its related services. These companies also require very high-skilled workers. However, the shortage of labor in these sectors is the primary reason these companies pay so well. “There is definitely a bidding war in the Bay Area for certain types of positions,” Chamberlain said. While this trend is industry-wide, all of the nine highest paying tech sector companies were located in California.

For instance, the growth in new technologies such as mobile devices has been so rapid it has been impossible for the labor market to keep up. Chamberlain suggested the shortage has been further compounded by restrictive immigration policies like the hard cap on H1B visas, which allow U.S. companies to bring specialty workers from overseas. These polices have put constraints on the supply of workers, further driving up competition.

None of the highest paying companies are in the manufacturing or goods producing industries that would have characterized a similar list several decades ago. The difference, according to Chamberlain, is that many of the jobs provided by the companies currently on this list are very difficult to outsource because they require relatively advanced judgements and non-routine tasks.

While paying high salaries perhaps makes a poor work environment more tolerable, it does not guarantee workplace satisfaction. All but one highest paying company received an overall employee rating greater than 3.2 out of 5, the average company rating from Glassdoor reviewers. CEO approval ratings were also strong in many of these companies, but not universally. More than 80% of reviewers in just six of the highest paying companies approved of their CEO.

To identify the highest paying companies in America, 24/7 Wall St. reviewed the median annual salaries in companies provided by Glassdoor. Employee ratings, CEO approval ratings, and the percentage of employees who would recommend the company to a friend also came from Glassdoor. Revenue figures and total headcounts for public companies came from financial filings. When available, company information for private companies was provided by the companies themselves.

These are America’s highest paying companies.