March 18 (Reuters) - Micron Technology forecast third-quarter revenue well above Wall Street expectations after posting a sharp jump in the second quarter on booming demand for memory chips used in artificial intelligence systems, while tighter supply drove record earnings.

But the company's $5 billion boost to its 2026 capital spending plan to keep up with the rising demand pulled the shares 5% lower in extended trading on Wednesday.

Micron aims to spend more than $25 billion this fiscal year and said this could rise further in 2027 as expansion in manufacturing facilities could result in construction-related expense climbing by more than $10 billion from a year ago.

Customers are committing to long-term data center investments as technology companies race toward artificial general intelligence. The resulting growth in AI data center capacity is fueling a sharp rise in demand for advanced memory and storage.

Micron MU.O, whose shares have gained more than 61% this year, is one of the only three major suppliers of high bandwidth memory chips essential to AI technology, along with South Korea's Samsung 005930.KS and SK Hynix 000660.KS.

"The step-up in our results and outlook are the outcome of an increase in memory demand driven by AI, structural supply constraints and Micron's strong execution across the board," CEO Sanjay Mehrotra said in his prepared remarks.

The chipmaker forecast third-quarter revenue of $33.5 billion, plus or minus $750 million, compared with analysts' average estimate of $24.29 billion, according to data compiled by LSEG.

It reported revenue of $23.86 billion for the second quarter ended February 26, beating expectations of $20.07 billion. Micron's board also approved a 30% increase to its quarterly dividend.