In comparison, the S&P U.S. Issued High Yield Corporate Bond Index has gained 6.3% year-to-date, with the SPDR Barclays High Yield Bond ETF (NYSEArca: JNK) up 5.7% this year. The S&P U.S. Issued Investment Grade Corporate Bond Index is up 1.7% year-to-date. The iShares iBoxx $ Investment Grade Corporate Bond ETF (NYSEArca: LQD), though, is down 2.0% this year.

The following chart reveals the taxable equivalent yield on tax-exempt investment grade bonds tracked in the S&P National AMT-Free Municipal Bond Index, the yield on investment grade corporate debt and 10-year U.S. Treasuries.

Source: S&P Dow Jones Indices

For information on munis, visit our municipal bonds category.

Max Chen contributed to this article.