NEW YORK ( TheStreet) -- As the array of ETF product offerings has expanded in recent years, the biotech space has seen significant activity. Currently, there are five biotech ETFs that have accumulated nearly $3.5 billion in aggregate assets. Each of these funds focuses on stocks in the biotechnology industry, and in many cases there is significant overlap between the top holdings. But as the relative performance of these funds so far this year has shown, the biotech ETFs available to U.S. investors are far from identical. Each of the biotech ETFs is up at least 6% so far in 2010, making this sector one of the best performers of the year. But the top-performing biotech ETF is up nearly 25% on the year, a significant return gap between funds that seem, at least on the surface, to be relatively comparable. >>Want More ETFs? Visit Our ETF Screener Page The significant performance gaps between these funds can be traced to the allocations made to a handful of biotech companies that have seen shares surge this year.