The three U.S. companies sitting on the most cash all come from the tech sector, and together they hold $391 billion in cash as of the end of 2015. That's almost a quarter of the $1.68 trillion held by the nation's non-financial corporations.

In fact, seven of the top 10 come from the technology space, according to a report from Moody's Investors Service comes from the technology space. Altogether, technology companies hold $777 billion in cash -- about 46% of the total across all non-financial industries.

"The top four cash-heavy U.S. industries remain technology, healthcare/pharmaceuticals, consumer products, and energy," said Moody's senior vice president Richard Lane in a press release. "These four industries currently hold a record $1.3 trillion, or 77% of total corporate cash and have accounted for more than 72% of the total every year since 2007."

But it's tech that's king, and Apple (NASDAQ: AAPL) leads the way with $215.7 billion in total cash, keeping the top spot it has held since 2009.

Apple holds the top spot by a significant amount. Image source: Apple.

What other tech companies are on top?

While Apple has a commanding lead when it comes to cash, Microsoft (NASDAQ: MSFT) was a clear second at $102.6 billion, followed by Alphabet (NASDAQ: GOOG) (NASDAQ: GOOGL), which was known as Google for much of 2015, at $73.1 billion. Cisco (NASDAQ: CSCO) was fourth with $60.4 billion, while Oracle (NYSE: ORCL) took fifth with $52.3 billion. Tech companies Intel (NASDAQ: INTC) and Qualcomm (NASDAQ: QCOM) came in ninth and 10th with $31.3 billion and $30.6 billion, respectively.

"While the concentration of cash among the top-rated cash holders continues to grow, so, too, has the portion held by the technology sector, which accounted for a record 46% of total cash in 2015, up from 41% in 2014," Lane said.

The tech-sector cash hoard is even more impressive when you consider that tech companies led all industries by share repurchases, buying back $118 billion worth of stock, according to Geekwire. They also spent big on research and development, acquisitions, and capital expenditures.

Not only did the tech sector dominate the 2015 reports, but Moody's also expects the industry will continue to dominate. The company "expects the technology sector cash concentration will grind higher over the next year because of the sector's strong cash flow generation and despite stronger returns of capital to shareholders," the firm wrote. Moody's also noted that in 2015, the technology sectors generated 63% of the total rated non-financial free cash flow in 2015, up from 37% in 2007.

Where's the money?

An ongoing political question in the United States has been whether companies should be allowed to bring back cash they hold overseas. The reason they don't, of course, is that if they repatriate the cash, they face a large tax bill.

Moody's estimates that Apple, Microsoft, Cisco, Google, and Oracle have $441 billion overseas, representing 87% of their cash, wrote Geekwire. That's a stunning amount of money, which makes it clear that corporate tax reform should be a bigger priority than it has been.

What's the cash being spent on?

To make the top 50 on the Moody's list, a company needs $6.12 billion in cash. The top 50 hold $1.14 trillion of the entire $1.65 trillion held by all U.S. companies in 2015, or about 70%.

For the top 50, capital spending fell by 3% to $885 billion, and net share buybacks fell 7% to $269 billion, according to Moody's. Dividends, on the other hand, were up 4%, growing to a record high of $404 billion. Acquisition spending hit a record $401 billion, up 43% from the previous year.

But there was a dark cloud in the report: For the first time since 2012, U.S. companies had less cash on hand than the sum total of their aggregate debt maturities over the next five years. In 2015, according to the report, that number dipped to 93%. While that's only likely to be a concern if the economy takes a major downturn, it's a number worth watching on a company-by-company basis for investors.