There isn't a completely objective criteria, from Wikipedia:

Federal Reserve Chair Ben Bernanke also defined the term in 2010: "A too-big-to-fail firm is one whose size, complexity, interconnectedness, and critical functions are such that, should the firm go unexpectedly into liquidation, the rest of the financial system and the economy would face severe adverse consequences."

NVIDIA currently makes up nearly 7.5% of the S&P 500 (not to mention that they have invested a lot in the other companies and those companies have invested in NVIDIA). If they were to suddenly be liquidated I'd say that would cause 'severe adverse consequences' to the economy.

And it would likely cause a ripple to other tech companies, which which make up roughly 1/3 of the entire US stock market.