NEW YORK ( TheStreet) -- Qualcomm ( QCOM) shares tumbled in premarket trading on Thursday as investors responded to the chip aker's weak third-quarter guidance. The San Diego-based firm, a key partner of Apple ( AAPL) and Samsung, comfortably beat analysts' forecasts in its second-quarter results, released after market close on Wednesday. Investors, though, were unimpressed by the company's guidance. Qualcomm expects third-quarter earnings between 83 cents and 89 cents a share. Revenue is forecast at $4.45 billion to $4.85 billion. Analysts polled by Thomson Reuters had estimated earnings of 90 cents on $4.8 billion in revenue. Shares of Qualcomm slid on the company's earnings announcement, and were down $2.43, or 3.62%, to $64.56 before market open on Thursday. EMC ( EMC), which reported first-quarter results early on Thursday, was another laggard as investors responded to the company's revenue number. EMC's sales came in at $5.1 billion, a shade below analysts' forecast of $5.12 billion. The storage giant's stock fell 84 cents, or 2.88%, to $28.30. Shares of Internet retail giant eBay ( EBAY), however, surged in premarket trading, climbing $3.28, or 9.14%, to $39.15 after the company's second-quarter results, released late on Wednesday. The online auctioneer comfortably beat Wall Street's earnings expectations, citing continuing momentum in its Marketplaces, PayPal and GSI Commerce businesses. eBay was also one of the most active Nasdaq tech stocks on Thursday on share volume of 1,449,148. F5 Networks ( FFIV) was another winner after flying past Wall Street's second-quarter estimates on Wednesday. The Seattle-based firm's stock rose $8.33, or 6.71%, to $132.54 before market open on Thursday. Shares of AMD ( AMD), which reports quarterly results after market close, were up 1% to $8.05. Microsoft ( MSFT), which is on deck to report third-quarter results late on Thursday, was down 0.26% to $31.06. --Written by James Rogers in New York. >To follow the writer on Twitter, go to http://twitter.com/jamesjrogers. >To submit a news tip, send an email to: firstname.lastname@example.org. Check out our new tech blog, Tech Trends. Follow TheStreet Tech on your wireless devices.