NEW YORK (TheStreet) -- The frenzy of mergers and acquisitions this year is showing no signs of letting up -- and some experts think that could be bad for stocks.

"The feverish pace of merger activity is a cautionary sign for U.S. stocks," David Santschi, chief executive of TrimTabs Investment Research, said in a statement. "Merger activity tends to peak around market tops."

Globally, M&A deals reached $2.28 trillion in the first half of 2015. That's the second highest total behind the record $2.59 trillion in the first half of 2007, shortly before the stock-market meltdown and global financial crisis.

Despite some similarities to that period, experts say the structure and nature of the current deals is materially different.

 "This is absolutely a different situation than 2007," said Robert Townsend, co-chairman of Morrison & Foerster's global M&A practice group. "This current M&A surge is driven more by strategics than private equity."

A strategic M&A deal refers to a company that purchases another firm to add a new product, extend its geographic reach, increase its customer base or bring in some strategic asset in a way that will boost both its top and bottom lines.

By contrast, many of the deals in 2007 involved private-equity players taking public companies private through leveraged buyouts, or LBOs. In general, strategic deals don't involve the enormous leverage that LBOs do.

 "In 2006 and 2007, we had a huge number of highly leveraged, all-cash transactions," said Adam Emmerich, a partner at Wachtell, Lipton, Rosen & Katz. "It's vastly different from the strategic deals that make up the bulk of M&A volume and activity" in 2015.

Still, there is some worry that companies may be overpaying for strategic deals if they don't result in increased growth.

After all, this is the sixth year of a bull market, where many market experts and economists openly question if stocks are overvalued. At the same time, interest rates remain near historic lows, giving buyers access to cheap and easy capital. All of that is a perfect storm for bidding wars where target companies could easily get taken out at lofty premiums to their already overheated stock prices.

"There are some sectors in the market that are probably overvalued, but I would say at this point it's a yellow light -- it's not a red light," Townsend said. "There's a lot more fundamental strength in the economy that is driving this and a lot more cash on the balance sheet of strategic investors."

Experts say deals could accelerate even more in the coming months as companies rush to get transactions done before the Federal Reserve starts to raise rates and capital becomes more expensive.

Emmerich is philosophical about what that means for stocks. "Can we call this a peak?" he asked. "M&A has historically been -- and will continue to be -- a cyclical activity."

But nobody knows for sure when a top is reached.

"If you knew when the market was peaking, you would be sipping a cocktail somewhere on your yacht in the south of France," he said.

This article is commentary by an independent contributor.