In about two weeks, one exchange-traded fund will do something highly unusual. It will mature.

The Guggenheim BulletShares 2011 Corporate Bond ETF (BSCB) is like most fixed-income ETFs in that it holds a diversified basket of bonds, passes the coupon payments on to shareholders as dividends and trades just like a stock.

But it takes the "fixed" part of fixed income literally. The bonds it holds mature in the same year. In fact, all but one of them has already been paid back into the fund, and the money parked in short-term Treasury bills. The remaining bond matures Thursday. Investors who hold to maturity should get their money back on Dec. 30.

There are other BulletShares portfolios that mature each year through 2015, some for high-quality (and lower yield) issues and some for high-yield (and lower quality) ones.

Bond investors have long been caught between two awkward choices. Individual bonds can add definition and stability to an investment portfolio, but it takes $500,000 or more to put together a diversified portfolio. And judging the creditworthiness of bond issuers is as difficult as assessing the growth prospects of stock issuers.

Traditional bond mutual funds address those problems. Minimum investments are low (often $1,000 to $10,000) and the portfolios are either professionally selected or designed to passively track indexes. But bond funds don't offer fixed returns or maturity dates.

A maturity date can be a key investor advantage. Bond prices can rise and fall according to changes in the economy or investor sentiment. An individual bond holder may choose to ignore short-term fluctuations and hold until the maturity date to receive his principal back in full. A bond fund holder sells shares at the current trading price, with no option to hold out for full return of principal.

Mutual fund companies call that a non-issue for long-term investors who reinvest bonds as they come due. For them, the cash flows of a bond fund should match pretty closely with those of individual bonds. But for an investor with a known future obligation, or one who simply takes comfort in a defined portfolio, maturity matters.

There has long been a third way to invest in bonds: unit investment trusts. These are bundles of bonds that are sliced into small units and sold to investors to be held to maturity. But UITs are often sold through brokers who work for commission, and as such they can carry significant up-front sales charges--often 3% or more. And investors who wish to sell early typically rely on the issuer to resell the units to other investors.

ETFs are usually recommended by advisers who work for a set fee, or else they're bought directly by investors, so fees are lower. Guggenheim charges 0.24% for its investment grade BulletShares and 0.42% for its high-yield ones.

At the moment, yields on investment-grade corporate bonds are very low, especially for the short-term bonds used in Guggenheim's portfolios. The soon-to-mature 2011 portfolio, which was launched about a year and a half ago, returned just 0.75% a year through November, not including fees. The 2017 portfolio has an average yield to maturity of 3.7%.

The high-yield or "junk" bond BulletShares have an average yield to maturity of between 5.3% for the 2012 portfolio and 7.8% on the 2015 one, not including fees.

In total, the funds have attracted about $750 million in assets, says Guggenheim managing director William Belden. Mr. Belden thinks the best opportunities are found in high-yield bonds with short maturities, for investors for whom the risks are appropriate.

Those risks include default by one or more issuers, of course. Mr. Belden says there have been no defaults so far, but high-yield bond issuers are weaker than firms with investment grade credit ratings, and a sharp economic downturn could impair their ability to pay. That risk is offset by diversification, with most BulletShares portfolios holding more than 70 different issues spread across sectors.

However, because the sector weightings are designed to reflect the broad bond market, the heavy financial exposure will be a turn-off for some investors. For the 2015 portfolios, the high-yield one has a 24% weighting in financials and the investment grade one, a whopping 53% weighting.

It's early to judge BulletShares, but the fees are reasonable, the maturity dates are a welcome innovation and the pending portfolio liquidation concludes what so far looks like a smooth maiden voyage. For investors who understand the risks, and who are willing to take on higher credit risk to secure more yield, the funds are worth a look.