Biotech ETFs are, in a word, hot.

The biotechnology industry, if it were a sector, would be the second-best performing one in 2020. Biotech stocks collectively have generated 21% total returns (price plus dividends) on average, lagging only technology, which is up 26% year-to-date. That's no surprise given the rush of investors into stocks developing treatments and vaccines for COVID-19.

But biotech ETFs are no flash in the pan. If you go back over the past decade, it has returned 524%. That beats every last sector, it beats the broader health care sector by 200 percentage points, and it's nearly double the S&P 500's (.SPX) total return in that same time frame.

There's clearly money to be made in the discovery of new treatments for anything, from COVID-19 to cancer, from rare diseases to everyday ailments such as asthma or eczema.

Biotech stocks carry substantial risks, of course, especially when it comes to smaller companies that might have just one or two revenue streams, or even no marketed products. While positive data from a drug trial could send their stocks soaring, a setback or failure can crush their returns, making them difficult buy-and-hold investments.

Biotech ETFs offer an answer. Instead of betting on individual drugs or companies, they allow you to buy the whole industry, spreading out risk across dozens or even hundreds of firms at a time.

Here are six biotech ETFs to buy. Some provide well-rounded access to the space, while others acutely focus on certain aspects of the space, such as cancer treatments or drugs to battle infectious diseases.

Data is as of Aug. 6. Yields represent the trailing 12-month yield, which is a standard measure for equity funds.

iShares Nasdaq Biotechnology ETF

Assets under management: $9.7 billion

Dividend yield: 0.2%

Expenses: 0.46%, or $46 annually for every $10,000 invested

The iShares Nasdaq Biotechnology ETF (IBB) is the largest of the market's biotech ETFs, and one of the most straightforward.

IBB tracks a market cap-weighted index of Nasdaq-listed biotech companies, which means the largest companies have the most effect on the fund's performance. The resulting 207-stock portfolio favors large-cap companies, which make up 50% of assets – roughly the same weight given to the fund's top 10 holdings. At the moment, Amgen (AMGN) is the largest holding at 8.2% of assets, followed by Vertex Pharmaceuticals (VRTX), Gilead Sciences (GILD) and Regeneron Pharmaceuticals (REGN).

Unsurprisingly, several of these names have ties to COVID-19 treatments or vaccines. Amgen, for instance, recently put its best-selling immunosuppressant, Otezla, into trials as a possible COVID-19 treatment. Gilead makes remdesivir, the antiviral that has gained FDA emergency-use approval for treating COVID-19. And Regeneron is trialing a vaccine.

IBB has very clear pros and cons. On the upside, because IBB is a bet on biotech's largest, most diversified and best-capitalized companies, these stocks won't suffer as much from a single failed clinical trial the way a smaller firm with a couple, one or even no approved products might.

But conversely, it won't benefit as much from the massive surges that smaller biotech stocks enjoy from positive trial success. Moreover, it might miss opportunities among NYSE-listed firms that other funds are able to hold.

SPDR S&P Biotech ETF

Assets under management: $6.0 billion

Dividend yield: 0.0%

Expenses: 0.35%

The SPDR S&P Biotech ETF (XBI), which tracks the S&P Biotechnology Select Industry Index, is a modified equal-weighted fund that addresses some of IBB's weaknesses.

While the 133-stock portfolio isn't nearly as wide as IBB's, the fact that it rebalances the portfolio every quarter to give all of its stocks equal say in the portfolio provides better diversification. It also gives smaller companies a larger say in performance; small caps make up two-thirds of XBI's weight, with another 25% in mid-caps and a small 8% in large caps.

Like IBB, XBI is a pure biotech play with very little overlap with traditional drug companies. It's also cheaper by 11 basis points (a basis point is one one-hundredth of a percentage point).

Top holdings at the moment include Novavax (NVAX, 3.6% of assets), Opko Health (OPK, 2.2%) and Invitae (NVTA, 1.9%). Opko has a test for COVID-19, and Novavax has a coronavirus vaccine in trials – so do other XBI holdings including Inovio (INO) and Moderna (MRNA).

Because most of its investments are in small companies, XBI can perform well during periods of consolidation. Stocks typically drop out of funds because they fail to meet some sort of size or quality requirement when the fund is reconstituted. But they also exit funds when they're bought out, creating a nice pop on their way out if they're purchased at a premium – a not-uncommon occurrence within this biotech ETF.

The downside? A focus on smaller companies can make XBI more volatile than IBB.

Loncar Cancer Immunotherapy ETF

Assets under management: $39.3 million

Dividend yield: 0.0%

Expenses: 0.79%

The companies in the Loncar Cancer Immunotherapy ETF (CNCR) are focused on finding cures for cancer, specifically using immunotherapy: treatments that turn the body's own defenses against the disease.

CNCR is based on the ETF provider's own Loncar Cancer Immunotherapy Index – an equal-weight index of companies in either production or clinical trials of cancer immunotherapies. Like XBI, the equal weighting draws attention to smaller companies but increases risk. But it does have a more even blend than XBI, at 36% large caps, 21% mid-caps and the rest in small-cap stocks.

Loncar's narrow focus makes this a necessarily concentrated portfolio, at 30 companies currently. Top holdings include the likes of gene editor CRISPR Therapeutics (CRSP), which does gene editing, Chinese biotech Beigene (BGNE) and Macrogenics (MGNX), which has a broad pipeline of anti-cancer drugs.

And while the focus is on cancer, yes, some of the CNCR portfolio also has COVID-19 ties. For instance, top holding BioNTech (BNTX, 5.0% of assets) is working on a vaccine with Pfizer (PFE). Another roughly 4% of the fund is dedicated to MRNA.

Principal Healthcare Innovators ETF

Assets under management: $103.2 million

Dividend yield: 0.0%

Expenses: 0.42%

The Principal Healthcare Innovators ETF (BTEC) is geared toward finding smaller, innovative companies that might get overlooked, with a focus on active investment in early-stage R&D.

The fund seeks out health care firms from the Nasdaq US Benchmark Index, but excludes the top 150 securities by market size, while also excluding companies with low trading liquidity. How it identifies "innovators," however, might seem a little unorthodox: Specifically, it seeks out "non-earners by means of having negative earnings over the prior 4, prior 8 or future 4 quarters at least half of the time." In other words, it selects companies with inconsistent or negative profits, the idea being that, for now, they're pouring every last cent into R&D.

BTEC then picks the best-ranked 150 to 200 companies based on its scoring measures, then weights those stocks by size, with no stock exceeding 3% at rebalancing, which happens twice a year. At the moment, Moderna is the top holding at 5.2% of assets, by virtue of its gains since the last rebalancing. Moderna, currently best-known for its COVID-19 vaccine candidate, was founded with the intention of building a large pipeline of drugs using messenger RNA technology.

The biotech ETF also holds BioMarin Pharmaceutical (BMRN, 3.0%), Seattle Genetics (SGEN, 3.0%) and Exact Sciences (EXAS, 2.9%), among others.

Invesco Dynamic Biotechnology & Genome ETF

Assets under management: $236.2 million

Dividend yield: 0.1%

Expenses: 0.57%

The Invesco Dynamic Biotechnology & Genome ETF (PBE), which came to market in 2005, is one of the oldest biotech ETFs you can buy.

PBE uses the Dynamic Biotech & Genome Intellidex Index as its benchmark. The Index weights 30 components by a variety of factors, including "price momentum, earnings momentum, quality, management action, and value." This has made it effective in limiting volatility, making this biotech fund best suited for conservative investors.

Invesco Dynamic Biotechnology & Genome ETF invests both in clinical-stage companies, as well as those with products that have already launched. While it's a concentrated portfolio, it's also a balanced one, by size, with 23% of assets in large caps, 30% in mid-caps and the rest in small caps. At the moment, Opko Health (6.7%), Amgen (5.0%) and Regeneron (5.0%) sit atop the hill. Assets are rebalanced each quarter.

ETFMG Treatments Testing and Advancements ETF

Assets under management: $74.6 million

Dividend yield: 0.0%

Expenses: 0.68%

The ETFMG Treatments Testing and Advancements ETF (GERM) is the youngest among these biotech ETFs, with inception just a couple months ago on June 17. But it has become one of the most popular ETFs traded on Robinhood, the millennial-heavy investment site, with several thousand accounts holding it.

ETFMG says that GERM "is designed to give exposure to the biotech companies directly engaged in the testing and treatments of infectious diseases." While it's a seemingly fitting ETF for the times – in the midst of a pandemic – the fund managers note that from January 2011 to January 2018 there were 38 epidemic events in the U.S. alone, and there are currently over 20 combined pandemics and epidemics affecting the world today.

In other words, GERM is far from just about COVID-19.

This is a split portfolio, with 68% of holdings in companies developing treatments for such diseases, while the other 32% of assets go to firms that help create and distribute testing solutions.

Top holdings in this roughly 55-stock portfolio include Novavax, which accounts for almost 11% in assets, as well as Moderna (5.5%). Emergent BioSolutions (EBS, 5.4%) is working with AstraZeneca to manufacture a COVID-19 vaccine candidate, and Quidel (QDEL, 5.3%) is a molecular diagnostics firm that produces a coronavirus antigen test. Other testing-focused holdings include the likes of Bio Rad Labs (BIO, 5.0%) and Laboratory Corp. of America (LH, 4.5%).