** Shares of bitcoin mining and data center firm Riot Platforms RIOT.O jump 5.3% to $15.42 premarket

** Activist investor Starboard Value urges RIOT to show a renewed sense of urgency to get more "material" AI deals completed

** Starboard says RIOT's shares have underperformed peers who have signed sizable AI deals

** "The recently announced transaction with Advanced Micro Devices is a positive signal and confirms our views regarding the intrinsic value of Riot's key sites, but it is a small proof of concept deal, and we, like you, expect significantly more," Starboard says

** Starboard increased its stake in RIOT, according to a filing on Tuesday to the U.S. Securities and Exchange Commission

** RIOT did not immediately respond to a Reuters request for comment

** As of last close, RIOT stock up 15.6% YTD

(Reporting by Arasu Kannagi Basil in Bengaluru)

((ArasuKannagi.Basil@thomsonreuters.com;))