State Street Global Advisors on Thursday launched an exchange-traded fund that invests in non-convertible preferred stocks.

The SPDR Wells Fargo Preferred Stock ETF (NYSEArca: PSK) comes with an annual expense ratio of 0.45 percent.

The new SSgA ETF will compete head-to-head against two others already on the market. Those are the PowerShares Preferred Portfolio (NYSEArca: PGX) and the iShares S&P U.S. Preferred Stock Index Fund (NYSEArca: PFF).

So far this year, PGX is up more than 20% and PFF has gained better-than 33%.

The new preferred ETF seeks to track the performance of the Wells Fargo Hybrid and Preferred Securities Aggregate Index. The index includes non-convertible preferred securities listed on the NYSE that are: priced at a par amount of $25; are rated investment-grade by Moody's or S&P; and have a minimum monthly trading volume during each of the last six months of at least 250,000 trading units.

According to a statement released by SSgA, PSK's underlying index provided exposure to more than 160 securities at the end of July.

Preferred securities have been an attractive area for more-income-minded investors lately. The stocks usually pay a fixed rate of distribution in addition to any potential gains an investor can receive from shares' price movements. Preferred shareholders also gain preferential treatment over common stock in bankruptcy proceedings or other legal disputes over distributions.