The stock market's been absolutely crazy in 2020, with huge ups and downs. Halfway through the year, those who invest in the S&P 500 (^GSPC -0.74%) are still down on the year, but most are breathing a big sigh of relief after having suffered far larger losses earlier in the year.

Even in the face of the downturn, there's a select group of stocks have risen dramatically so far in 2020. Here, we'll look at the three top performers with an eye toward figuring out what the future's likely to bring for them.

DXCM Chart

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DexCom, up 86%

In some ways, it's questionable whether DexCom (DXCM -3.78%) truly deserves a place on this list. The company has been public for 15 years, but it just joined the S&P 500 Index in May.

DexCom's success has come from its revolutionary products. The medical device maker is behind the STS Continuous Glucose Monitoring System, which helps diabetes patients get continuous real-time glucose measurements and can provide alerts if glucose levels reach troubling levels. Unfortunately, diabetes is affecting more patients than ever, and that's made DexCom a key provider in helping people fight the disease without having to do repeated glucose checks on their own all the time.

Device, readout, smartphone, and watch all showing blood sugar monitoring.

Image source: DexCom.

Investors like DexCom because demand for its products isn't sensitive to economic conditions. That's made it a solid play, and the growth potential has helped give DexCom extraordinary performance as well.

Regeneron Pharmaceuticals, up 66%

The biotech industry has been a hotbed of interest in 2020, because many companies in the space have looked for ways to apply their therapies to fight the COVID-19 pandemic. Regeneron Pharmaceuticals (REGN -0.33%) is one of those companies. It's gotten plenty of growth recently as well from non-coronavirus treatments like eye disorder treatment Eylea and eczema drug Dupixent.

Investors have their eyes on REGN-COV2, a COVID-19 treatment candidate that seeks to prevent the coronavirus from entering host cells. Human trials of REGN-COV2 began just last month, so it'll be a while before data becomes available. However, with a history that includes the successful Ebola virus treatment it developed, Regeneron has medical professionals feeling optimistic about the company's prospects for coming out with a sequel.

PayPal Holdings, up 64%

COVID-19 has had a hugely disruptive impact on the economy, but there've still been some companies that have done well during the pandemic. PayPal Holdings (PYPL -0.98%) has benefited from greater adoption of e-commerce channels, for which customers generally need electronic payment systems like PayPal's to make purchases.

PayPal faces plenty of competition, but it has worked hard to distinguish itself from the crowd and make itself a leader in the electronic payments industry. Most recently, PayPal has stressed the development of contactless payment features, which will allow both merchants and consumers to pay without having to actually touch any surfaces at a storefront. That could prove more important than ever for health and safety purposes. It's also persuaded some businesses to shift to PayPal, and that comes at the same time that online checkout market share for the payment network has been on the rise. With industry-leading experience and a strong brand, PayPal has staying power in the cutthroat electronic payment space.

What's next for the S&P?

Even with the S&P still down for the year, many investors are optimistic about the future. That's particularly true for these three high-growth stocks. PayPal, Regeneron, and DexCom all have the potential to keep riding the wave higher even if the broader stock market stays in the doldrums.