PowerShares QQQ (NasdaqGM: QQQ) was set for a slightly lower open Thursday following the previous session’s wipeout as top holding Apple (NasdaqGS: AAPL) lost nearly 3% following a brief foray above $400 a share.

Apple shares have been on a tear and recent blowout earnings further stoked bullish sentiment on the seller of iPhones and iPads. The stock is up nearly 20% over the past month.

Apple accounts for 13.9% of PowerShares QQQ, which tracks the Nasdaq-100. The exchange traded fund slipped 2.6% in Wednesday’s broad market sell-off, and was fractionally lower in Thursday’s premarket.

Apple is a profit machine and had the largest cash reserves of any U.S. company in 2010, according to a report. USA Today reports that the tech sector has more cash on hand than any other. The tech industry boasts about $264 billion in cash reserves at the end of 2010. [Tech ETFs: Are Valuations Running Out of Hand?]

Moreover, according to Moody’s, Apple has about $59.7 billion in cash reserves and reported $76.2 billion in cash holdings, in the latest quarterly report.