Advanced Micro Devices Inc. shares rose Thursday after an analyst said the chip maker is probably benefiting more from cryptocurrency mining-related sales than it is saying.

AMD AMD, -2.11% shares rose 2.9% to $12.53 in afternoon trading, after touching an intraday high of $12.68. Shares are up 22% for the year so far, compared with a 4.7% gain in the S&P 500 index SPX, -1.11% and a 9.4% gain in the PHLX Semiconductor Index SOX, -1.51% .

Susquehanna Financial Group’s Christopher Rolland, who has a neutral rating on AMD and Nvidia Corp. NVDA, -2.20% , said the two companies “likely benefited” from more than $500 million in Ethereum-related sales of their graphics-processing units in the fourth quarter of 2017. Both AMD and Nvidia played down the role of cryptocurrency mining sales in their most recent quarterly-earnings presentations. Nvidia shares traded between slight gains and losses, and are up 16% for the year.

Read:Nvidia, AMD close lower as cryptocurrency miners’ thirst for graphics chips doubted

Rolland said the trend for graphics cards continued for the first few weeks of the year and probably resulted in more than $200 million in GPU sales in that time.

Cryptocurrency traders have been enduring a wild ride lately with the price of bitcoin BTCUSD, -1.58% having fallen from its all-time highs of above $19,000 back in December to below $10,000 on Wednesday. At last check, bitcoin is up 5% at $11,686. Ether, the cryptocurrency running on the Ethereum network, has similarly fallen from its recent highs, having traded north of $1,400 as recently as Jan. 13 and dropping below $900 just a few days later. Ether, at last check, was up 3.7% at $1,052.

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Even with the drop in ether, Rolland said that “mining profitability remains among the highest in history,” and that retail markups for card remains at an all-time high, suggesting strong demand and short supply.

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“We believe the confluence of these factors portends upside to both AMD’s and NVDA’s C4Q17 results (and perhaps 1Q18 guidance),” Rolland said. “However, we also note substantial longer-term risks for both companies as mining profitability may have induced ‘false purchases’ of more and higher-priced cards.”

It’s on that false purchases possibility, if ether prices decline, that Rolland lowered his price target on AMD to $13 from $15.

Other analysts have reported that mining on the Ethereum blockchain could move beyond the use of GPUs in the first half of the year, with chips such as ASICs becoming more common, as they are for bitcoin and other more mature cryptocurrencies. RBC Capital Markets analysts said earlier this year that there are plenty of newer cryptocurrencies for which miners could use GPUs, including monero, bitcoin gold and ethereum classic.