Exchange-traded funds are all the rage as investors seek out low-cost ways to get exposure to the stock markets. The popularity of these funds is also increasing at The Charles Schwab Corporation (SCHW), the San Francisco-based discount broker.

Speaking during a recent Morningstar ETF conference that was covered by, Heather Fischer, vice president of the ETF and mutual fund platforms at Charles Schwab, told the crowd that the company continues to see ETF demand grow, which she said is not surprising. "We recently did our annual ETF investor study, and the results tell us that they have long been interested in ETFs and that enthusiasm continues," Fischer said.

According to the Schwab executive, when the brokerage started asking investors five or six years ago about their feelings on ETFs, 16% said that their portfolios were in ETFs. That has increased to 27%. What's more, investors are predicting that this number will grow to 33%. "It's a continued powerful high trajectory," Fischer said at the conference. Fischer noted that millennials are particularly interested in ETF investing, with 60% to 65% signaling that they will include ETFs into their portfolios. "[Millennials] are really leaning in," Fischer said. "So the numbers overall are strong, but they are powerfully strong with millennials."

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According to ETF Trends, Charles Schwab had ETF assets of $380 billion at the end of September, up from $292 billion in the same period a year ago, which marks a 30% year-over-year increase. Schwab's registered investment advisor clients had ETF assets of $201 billion in September, up 31% from the $154 billion at the end of September of 2016, representing the largest jump in demand from a year-ago period. Retail investors' ETF assets jumped 27% to $132 billion from $104 billion, while retail traders' ETF assets increased 37% to $47 billion from $34 billion, noted ETF Trends.

The increase in investments going into ETFs comes at a time when Charles Schwab is trying to make more inroads on that side of its business. In October, Schwab announced a new exchange-traded fund that takes aim at BlackRock, Vanguard and State Street thanks to a lower expense ratio. The Schwab 1000 Index ETF (SCHK​) provides investors with a low-cost way to obtain exposure to the 1,000 largest stocks in the U.S. The new ETF, which has an operating expense ratio of 5 basis points, or 0.05%, began trading on Oct. 11 and is available through the company's commission-free ETF program in which it offers investors access to more than 200 ETFs that do not have commissions attached to them.