Many investors in exchange-traded funds have enjoyed a nice rebound in growth stocks to start 2023, but a look under the hood of some of those ETFs will show that their holdings are now concentrated in a few key names. Tech stocks with healthy cash flow have been the big winners so far this year, and those names are also dominating the growth indexes. "The combined weight of AAPL + MSFT in the Russell 1000 Growth index is nearing 25%. Each individual weight is over 10%, the first time two names have held that kind of influence in the benchmark using 28-years of data," Strategas ETF strategist Todd Sohn said in a note to clients on Tuesday. That type of heavy weighting in a handful of stocks tends to make investors nervous, especially with many Big Tech companies set to report earnings over the next week. "On one hand, continued strength from up the scale can benefit passive ETF investors, but on the other, concentration risk continues to grow," Sohn added. One way to dial back your exposure to mega-cap tech while keeping bets on growth is through mid-cap growth ETFs, according to Citi. "US Mid Cap Growth appears to be an attractive means of narrowing our portfolio's Growth underweight after we missed the Mega Cap Growth trade driving the large cap indices during Q1. Its blend of attractive fundamentals and solid growth outlook fit our model portfolio's quality and defensible growth theme," strategist Scott Chronert said in a Friday note. Another benefit of the mid-cap growth area is that is not as reliant on tech stocks as the large-cap growth bucket, he added. The Citi note highlighted several ETFs that track the mid-cap growth space, including the iShares Russell Mid-Cap Growth ETF (IWP) , the Vanguard Mid-Cap Growth ETF (VOT) , and the Invesco Nasdaq Next Gen 100 ETF (QQQJ) . These funds do have less concentrated exposure than other popular growth ETFs. The IWP, for example, has a combined weight of about 29% in technology and communications sectors. That is well below the roughly 48% combined weight of those sectors in the iShares Russell 1000 Growth ETF (IWF) . The QQQJ also has more than 40% of its holdings in tech and communications, but its single largest position is ON Semiconductor at 2.33%. The IWF has six different stocks with larger weightings, including both share classes of Alphabet. — CNBC's Michael Bloom contributed to this report.