** Shares of Qorvo QRVO.O up 7.1% at $78.82 premarket
** Activist investor Starboard Value has built 7.7% stake in chipmaker valued at around $500 mln, Wall Street Journal reports
** Stake is expected to be revealed in securities filing Friday morning - report
** Starboard is seeking changes to boost company's lagging share price - report
** Starboard and Qorvo did not respond to Reuters' requests for comment
** QRVO down 27% in the past 12 months
(Reporting by Medha Singh)
((medha.singh@thomsonreuters.com))