Last week brought an avalanche of earnings reports from the largest U.S. banks and investors apparently did not like what they heard as the Financial Select Sector SPDR (NYSEArca: XLF) slipped 1.5%.

Investors’ tepid reaction to big bank earnings updates was, in part, due to a fourth consecutive week of losses for U.S. stocks. Citigroup (NYSE: C) beat analysts’ estimates while rivals J.P. Morgan Chase (NYSE: JPM) and Wells Fargo (NYSE: WFC) fell short of Wall Street expectations. However, that is not stopping some investors from warming up to financial services ETFs.

Although $588.3 million was pulled from XLF last week, investors added nearly $43 million to the PowerShares KBW Bank Portfolio (NYSEArca: KBWB), making the ETF top asset gather among all PowerShares ETFs last week, according to issuer data.

Home to 24 stocks, KBWB, at least on the surface, appears to be a direct play on money center banks. Bank of America (NYSE: BAC), Citigroup, Wells Fargo and J.P. Morgan Chase are the ETF’s top-four holdings, combining for about 34% of the ETF’s weight. However, there is more to this ETF’s story and includes substantial leverage to the Federal Reserve’s interest rate outlook.

Although KBWB features ample exposure to the largest U.S. money center banks, investors in the ETF would do well to listen closely to what the Federal Reserve is saying about interest rates. The reason being is that about half of the ETF’s 24 holdings are regional banks and that does not include the super-regionals held by the fund, such as U.S. Bancorp (NYSE: USB) and SunTrust (NYSE: STI). [A Bank ETF on the Rise]