Last year, cryptocurrencies burst onto the scene like no other asset class ever has. Over the span of 12 months, the aggregate value of digital currencies soared almost $600 billion, which in percentage terms worked out to more than 3,300%. This was probably the best single-year return for any asset class in history, and we may never see anything like it again.

However, not everyone who's made money off the cryptocurrency craze has done so as a traditional investor. Some individuals and businesses have made veritable fortunes by "mining" cryptocurrency.

Graphics processing units set up to mine cryptocurrency.

Image source: Getty Images.

The rise of cryptocurrency mining

Cryptocurrency mining describes the process by which persons and/or businesses with high-powered computers and servers compete against one another to solve highly complex mathematical equations that are the result of the encryption designed to protect transactions on a blockchain network. The first to solve a group of equations and verify that those transactions (known as a block) are true -- i.e., that the same virtual token wasn't spent twice -- receives what's known as a "block reward." This reward is paid out in tokens of the virtual currency that's being proofed.

For example, bitcoin currently has a block reward of 12.5 tokens. This means that the first person, group of individuals, or business to validate a block of transactions will receive 12.5 bitcoin tokens. With the world's most valuable cryptocurrency currently hovering just above $8,000 per coin, we're talking about a more than $100,000 haul for cryptocurrency miners who are successful in beating others to the proverbial punch.

... and the risks

Of course, there are other factors that need to be kept in mind. There are exorbitant costs involved with crypto mining, too. This is a highly electricity-intensive practice that uses dozens, hundreds, or thousands of hard drives, processing units, and servers, to solve complex equations. Not only does this rack up quite the electric bill, but it creates a lot of heat, which may also require a cooling system. Also, hardware becomes obsolete rather quickly, requiring miners to regularly upgrade their equipment to remain competitive.

What's more, not all virtual currencies are mineable. While well-known cryptocurrencies like bitcoin, Ethereum, Bitcoin Cash, Litecoin, Monero, and Dash are mineable, others, such as Ripple, EOS, Cardano, Stellar, IOTA, and NEO, have a different method of transaction validation known as proof of stake. With proof of stake, owners of cryptocurrency are randomly chosen to validate transactions. There is no competition, and more importantly, virtually no added electricity costs.

A physical bitcoin lying atop a messy pile of hundred dollar bills.

Image source: Getty Images.

The top cryptocurrency mining stocks

Though cryptocurrency mining has been profitable, it's clearly not feasible for everyone. Nevertheless, there are ways investors can gain exposure to crypto mining, should they choose, through the stock market. Here are four top cryptocurrency mining stocks that have either direct or partial exposure, based on sales, to the industry.

NVIDIA and Advanced Micro Devices

Perhaps the most prominent names of the bunch are NVIDIA (NASDAQ:NVDA) and Advanced Micro Devices (NASDAQ:AMD), which are best known for their graphics card and PC-based microprocessors, respectively. Neither company has exactly been forthcoming with regard to how much of their sales are tied to cryptocurrency mining, but each company has clearly benefited in recent quarters from the sale of graphics processing units (GPU). NVIDIA's full-year results pointed to 41% year-over-year sales growth, with Advanced Micro's sales up 25% on an annual basis. 

In fact, demand for GPUs has been so strong that the price of graphics cards, new and old, has been shooting higher. This actually creates a bit of a conundrum for NVIDIA and AMD, as Advanced Micro Devices is more commonly known. The core customers for both companies are avid gaming enthusiasts and enterprise clients. If crypto mining demand continues to pluck supply from the market, the high price for graphics cards could cause a rebellion among NVIDIA's and AMD's core customers. Then again, if these companies create a product specifically for crypto mining, they'll drive down prices by increasing supply and squash the sales and margin boost they've recently experienced.

While both companies certainly have a lot going on beyond the cryptocurrency mining industry, it's possible that their share prices could reflect the ebbs and flows of virtual currency token prices, so it's something to keep in mind.

Messy stacks of physical silver and gold Ether coins.

Image source: Getty Images.

Taiwan Semiconductor Manufacturing Company

Another burgeoning cryptocurrency mining stock that isn't exactly keen on divulging the percentage of its sales tied to mining is Taiwan Semiconductor Manufacturing Company (NYSE:TSM). Last week, TSMC reported strong first-quarter operating results that included a 6% increase in sales from the prior-year period, as well as its single-best sales month in history in March ($3.5 billion). C.C. Wei, TSMC's president and co-CEO, specifically said that "these results were mainly driven by strong demand from high performance computing such as cryptocurrency mining." 

In addition, Coindesk notes that Chinese mining hardware maker Bitmain, a client of TSMC, unveiled its next-generation, ASIC (application-specific integrated circuit)-based, Ethereum mining equipment called Antminer E3 in early April. The unit, which has a list price of $800, is set to ship in July. Bitmain's need for ASIC chips to satisfy demand for Antminer E3 may very well be the reason TSMC experienced a surge in sales during March and in Q1 as a whole. 

However, the downdraft in bitcoin and other crypto token prices in 2018 has certainly cast a shadow on industry demand moving forward. Having previously forecast sales growth of 10% to 15% in 2018, TSMC also lowered its sales growth expectations to 10% for the current year on uncertainty in the crypto mining space. Like NVIDIA and AMD, TSMC's share price may be adversely impacted if cryptocurrency prices continue to sink. 

Graphics processing units connected to mine virtual currencies.

Image source: Getty Images.

HIVE Blockchain Technologies

Now, if you want as much cryptocurrency mining exposure as possible without actually running your own mining operation, there's the over-the-counter exchange-listed HIVE Blockchain Technologies (NASDAQOTH:HVBTF). This publicly traded cryptocurrency mining firm is currently in the process of ramping up its operations in Sweden and Iceland, and envisions generating approximately $150 million in annual revenue from its operations. Sweden and Iceland offer commercial kilowatt-per-hour electricity prices that are well below the European average. Plus, these are relatively temperate nation's, which may aid in keeping mining equipment cool.

Now here's where things really get interesting. Despite being a crypto mining start-up, HIVE Blockchain already turned a profit in its most recently reported quarter. Sure, the $149,724 in profit was negligible and resulted in $0.00 in earnings per share, but that profit was derived from just over $3 million in quarterly sales. Presumably, HIVE could generate more than 10 times this each quarter when fully ramped up.

The wildcard here is what'll happen to cryptocurrency prices. You see, HIVE Blockchain isn't necessarily selling all of the Ethereum, Ethereum Classic, and ZCash tokens that it's mining. It hangs on to some of these coins in the hope that they'll appreciate in value. Thus, investing in a company like HIVE gives an investor direct access to crypto mining margins, as well as the movement in a handful of popular digital currencies. 

Like the other companies above, there are also plenty of risks. Given that its business is entirely devoted to crypto mining and lacks sales diversity, investors would need to understand that if virtual currency prices fall considerably, their investment in HIVE could dive. Furthermore, in order to raise capital, it wouldn't be surprising if HIVE Blockchain diluted existing investors with bought-deal offerings. These are the risks that stock investors would have to endure if they wanted direct access to a publicly traded cryptocurrency mining stock.

Sean Williams has no position in any of the stocks or cryptocurrencies mentioned. The Motley Fool owns shares of and recommends Nvidia, but has no position in any cryptocurrencies mentioned. The Motley Fool has a disclosure policy.