** Shares of chipmaker Marvell Technology MRVL.O down 15.8% at $75.89 in premarket trading

** MRVL forecast fiscal first-quarter revenue of $1.875 bln, plus or minus 5%, compared with an estimate of $1.87 - data compiled by LSEG

** The company forecasts adjusted profit of 61 cents/share, plus or minus 5 cents, for fiscal Q1; analysts expected profit of 60 cents/share

** Morningstar analysts said the stock drop was due to results and the forecast meeting estimates, rather than beating expectations

** "We are downgrading the stock to a HOLD as we believe investors' expectation are too high and it lacks financial leverage as AI ASIC business could pressure its gross margin further" - Summit Insights Group

** Up to last close, the stock had risen ~14%, compared with a ~6% decline in the Philadelphia SE Semiconductor Index .SOX in the past 12 months

(Reporting by Akash Sriram in Bengaluru)

((Akash.Sriram@thomsonreuters.com; https://twitter.com/hoodieonveshti;))