Adds chart and CEO comments in paragraphs 6, 7 and 8

By Ozan Ergenay and Danilo Masoni

GDANSK/MILAN, May 27 (Reuters) - Shares of European chipmaker X-FAB XFAB.PA surged on Wednesday after retail buying tied to a viral social media post, in the latest sign of speculative trading in semiconductor stocks.

The Paris-listed stock rose as much as 76%, briefly valuing the company at about 2.06 billion euros ($2.40 billion), a record high. It later trimmed gains but was up 38% by 1322 GMT, taking this year's total gains to 141%.

Traders said there was no obvious corporate news behind the move.

"It's being pushed on X," said Stephane Ekolo, equity strategist at TFS Derivatives in London.

The post, from the X handle Serenity, highlighted X-FAB as an "interesting long idea" linked to photonics and power semiconductors.

X-FAB CEO Damien Macq said the company knew of no undisclosed development that would explain the rise.

"We have observed the recent increase in our share price and trading volumes. The company is not aware of any undisclosed material developments that would warrant disclosure at this time," Macq told Reuters via email.

Retail flows appeared to dominate activity, with X-FAB among the most traded stocks on Germany's Tradegate platform, ranking second behind U.S. chipmaker Micron Technology MU.O and ahead of Germany’s Infineon IFXGn.DE.

The same X handle, also known as @aleabitoreddit, was previously linked to sharp gains in UK computer hardware firm Raspberry Pi RPI.L in February. Since then, its followers have grown to more than 411,000 from around 58,000.

Semiconductor shares were already rallying on expectations that artificial intelligence will support demand. Macq said X-FAB remained focused on automotive, industrial and medical markets, including photonics and data centre applications.

SK Hynix 000660.KS topped $1 trillion in market value for the first time on Wednesday, joining memory chip peers Samsung Electronics 005930.KS and Micron MU.O.

($1 = 0.8593 euros)