The Technology Select Sector SPDR (NYSEArca: XLK), the largest technology exchange traded fund by assets, is up about 17% year-to-date, a gain that is more than double that of the S&P 500. It is just one example, but it underscores the point that technology, the largest sector weight in the S&P 500, is the best-performing part of the U.S. equity market this year.

Rivals to XLK include the Fidelity MSCI Information Technology Index ETF (NYSEArca: FTEC) and the Vanguard Information Technology ETF (NYSEArca: VGT). Apple Inc. (NASDAQ: AAPL) is the largest holding in all three ETFs.

While stocks such as Apple, Google parent Alphabet Inc. (NASDAQ: GOOG) and Facebook Inc. (NASDAQ: FB) are surging, some investors are becoming concerned about the technology sector’s valuations and are departing the corresponding ETFs as a result.

XLK “had outflows of $527.4 million on Tuesday, the biggest one-day redemption of any ETF on the market by far, according to FactSet data. It was also the largest one-day outflow for the fund, which has $17.4 billion in assets, since Jan. 31,” reports Ryan Vlastelica for MarketWatch.

Technology companies are still sitting on cash hoards that can be deployed in ways to improve value with investors. We are already seeing an increase uptick in company share buybacks and tech firms are now even issuing dividends.

The PowerShares QQQ (NasdaqGM: QQQ), which tracks the tech heavy Nasdaq-100, resides near record highs and has recently been adding assets. QQQ’s year-to-date inflows are $2.44 billion, more than any other PowerShares ETF.

“While there is not a perfect correlation between flows and investor intent—for example, heavy inflows can indicate that investors are building short positions, or betting on a decline—pronounced outflows can be a signal that market participants are closing out positions,” according to MarketWatch.

As MarketWatch notes, the PowerShares NASDAQ Internet Portfolio (NasdaqGM: PNQI) has also seen some modest departures. Investors pulled $5.2 million from PNQI on Tuesday. That ETF allocates almost a quarter of its combined weight to Alphabet, Amazon.com Inc. (NASDAQ: AMZN) and Netflix Inc. (NASDAQ: NFLX).

PNQI provides exposure to the growth style of the increasingly important internet segment, especially the quickly growing e-commerce or online consumer discretionary segment. The ETF holds 89 stocks, including some companies based outside the U.S.

For more news and strategy on the Technology market, visit our Technology category.

Tom Lydon’s clients own shares of Apple, Facebook and QQQ.