The financial sector hasn't exactly performed well during the COVID-19 pandemic. Even after the recent vaccine-fueled rebound, the Financial Select Sector SPDR ETF has produced a total return of negative 4% so far in 2020, dramatically outperforming a 17% return in the S&P 500.

Fintech giant Square (SQ 0.42%) is a big exception to the sector's underperformance. In fact, Square's stock price has more than tripled this year. A $1,000 investment in Square at the start of 2020 would be worth $3,327 as of Dec. 7.

Square card reader attached to smartphone.

Image source: Square.

This is just the latest in a strong history of outperformance. Here's how investors who get in even earlier did:

If you invested $1,000 in Square on this date: Here's how much you'd have now: 
Jan. 1, 2020 $3,327
Jan. 1, 2019 $3,711
Jan. 1, 2018 $6,004
Jan. 1, 2017 $15,300
Jan. 1, 2016 $15,900

Data source: yCharts. Returns as of 12/7/2020.

Why has Square done so well, and is there more upside ahead?

Simply put, Square's business has thrived during the pandemic. Square's net revenue in the third quarter was up by a staggering 148% year over year, and more important for future growth, its Cash App user base has doubled over the past year.

The Cash App is by far the most exciting driver of future growth, and although the company has done a great job of building out and monetizing its ecosystem (Cash App gross profit nearly tripled year over year), it is still in the early innings. In addition to the core person-to-person payment functionality and stock trading and bitcoin buying capability, there are many other financial services Square could potentially add.

In a nutshell, Square has delivered incredible returns for investors in 2020, and rightfully so. And if it can keep its revenue and user base growing at anything close to the current rate, there could be much more upside ahead.