Bill Gates — the second richest person in the world with a current net worth of $108.8 billion, according to Forbes — says his extreme wealth is not fair.

"The distance between top and bottom incomes in the United States is much greater than it was 50 years ago," Gates wrote in a blog post reflecting on 2019 published Tuesday. (Indeed, American income inequality is at its highest level in decades, according to U.S. Census Bureau's Gini index.)

"A few people end up with a great deal—I've been disproportionately rewarded for the work I've done—while many others who work just as hard struggle to get by," he wrote.

To solve the problem, Gates said the U.S. government should raise taxes that affect the wealthy.

"I'm for a tax system in which, if you have more money, you pay a higher percentage in taxes. I think the rich should pay more than they currently do, and that includes Melinda and me," Gates wrote, referring to his wife.

Specifically, he said there should be a higher capital gains tax (a tax on money made on investments), which would disproportionately affect the wealthy. None of the richest people in the world have made their fortunes solely through a salaried job, and for that reason Gates believes the government "should shift more of the tax burden onto capital" rather than labor.

"I don't see any reason to favor wealth over work the way we do today," he wrote. It's "the clearest evidence I've seen that the system isn't fair," he said.