Share buybacks have been in the news lately as hedge fund manager David Einhorn sues Apple (NasdaqGS: AAPL) in an effort to force the tech giant to return some of its nearly $140 billion cash hoard to investors.

Yet flying under the radar in recent years is an ETF focused on share buybacks that has nearly doubled the return of the S&P 500 since 2008.

PowerShares Buyback Achievers Portfolio (NYSEArca: PKW) has posted a five-year annualized return of 8.5%, compared with 4.8% for the S&P 500.

“With interest rates at record lows, corporate cash balances at record highs, and tax policy visibility as low as it could ever be, corporate spending on buybacks came in 50% higher in 2012 than the average in the preceding decade,” ETF Base reports. [Buyback ETF in Focus as Companies Repurchase More Stock]

“Buybacks aren’t as visible as dividends, and thus their impact on stock prices isn’t immediately observed by investors,” it notes. “This leads to controversy among investors who feel that buybacks might not be as rewarding to shareholders as continued reinvestment in the business, dividends, or acquisitions. Studies point to higher returns for companies that repurchase shares, however.”

The buyback ETF holds about $240 million in assets under management.

To become eligible for inclusion in the tracking index, a company must be incorporated in the U.S., trade on a U.S. exchange and must have repurchased at least 5% or more of its outstanding shares for the trailing 12 months, according to sponsor Invesco PowerShares.

PKW’s top sector allocations are consumer discretionary at 35.9%, financials at 19% and information technology at 16.4%. The concentration in consumer discretionary stocks has provided a lift. [Retail ETFs Making New All-Time Highs]

A related fund, TrimTabs Float Shrink ETF (NYSEArca: TTFS), is an actively managed fund that focuses on companies that are lowering the number of shares outstanding.

Paul Britt at Index Universe takes a look at the two ETFs which provide exposure to the buyback play, but differ greatly despite their common strategy.

“Believers in the buyback play offer a simple rationale: Who better than the firm’s own management would have a solid grasp of the company’s prospects in the competitive landscape and therefore its true value relative to its market price?” he wrote.

An ETF that also zeroes in on this theme is Guggenheim Insider ETF (NYSEArca: NFO). [ETFs That Focus on Share Buybacks]

PowerShares Buyback Achievers Portfolio