Three tech giants soared after earnings Thursday, and some CNBC "Fast Money" traders believe it could be time to sell rather than buy.

Shares of Amazon, Google holding company Alphabet and Microsoft all jumped at least 9 percent in extended trading on strong results. At their after-hours peaks, both Amazon and Alphabet shares would beat all-time highs.

Investors may want to avoid buying the news, said trader Dan Nathan.

"That's kind of dangerous to me," he said, adding that their strong performance may be masking laggards in the tech-heavy Nasdaq 100 index.

Alphabet

Alphabet posted earnings of $7.35 per share on revenue of $18.68 billion, beating analysts' expectations on both metrics. The company also announced it had authorized a share repurchase.

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Traders Guy Adami and Steve Grasso both said the stock should continue higher from here. In after-hours trading, the Class A stock hit about $742 per share.

Investors could shed some of their position when it reaches $750 per share, trader Brian Kelly said.

Amazon

E-commerce giant Amazon posted its second-straight quarterly profit, boosted by strong North American sales and cloud computing growth. It easily beat analysts' estimates, reporting earnings of 17 cents per share, while the Street had expected a loss of 13 cents.

"This was a ridiculously good quarter," said trader Guy Adami.

Read MoreAmazon shares spike 10% on huge earnings beat

However, he said, shareholders may want to sell some of their stake.

Disclosures:

Dan Nathan

Dan is long AMAT Jan call spread, PYPL Oct call calendar, BA Oct put spread, INTC Dec put spread, XLF Dec put spread, IWM Dec put spread, XLI Dec put spread, TWTR

Steve Grasso

Steve is Long AAPL, BA, BAC, CC, DD, DIS, DECK, EVGN, FIT, KBH, MJNA, MBLY, MU, OLN, PFE, PHM, T, TWTR, GDX firm is long IBM, AMZN kids own EFA, EFG, EWJ, IJR, SPY

Brian Kelly

Brian Kelly is long BBRY, GLD, Bitcoin, Silver, TLT, US Dollar; he is short Yuan, British Pound, Euro, Yen, EEM, EWC, EWU, EWG, SPY

Guy Adami

Guy Adami is long CELG, EXAS, INTC, Guy Adami's wife, Linda Snow, works at Merck.