Stm Grp. Share News (STM)

* STOXX 600 down 1 pct

* Tech sector falls 1.6 pct

* Chipmakers STMicro, Infineon, ams tumble

* Sodexo drops on downgrade

* Mediaset jumps after Sky deal(Updates prices, adds details, quotes)

By Helen Reid

LONDON, April 3 (Reuters) - European stocks tumbled onTuesday as investors entered the second quarter in a febrileatmosphere of trade tensions and mounting pressure on bigtechnology companies.

The pan-European STOXX 600 fell 1 percent, whileGermany's DAX declined 1.4 percent, with industrials,financials and healthcare stocks the biggest weights.

The tech sector dropped 1.6 percent, weighed bychipmakers after an overnight report that Apple plans to replaceIntel chips in Macs with its own.

The index has fallen 8 percent in the past three weeks asanxiety grew over big tech companies with the focus onFacebook's use of data, and regulation of Amazon.

Reports of Apple increasingly going down the "insourcing"route have dented shares in Apple suppliers around the world,most notably Europe's Dialog Semiconductor which hasshed more than 60 percent in the past year.

On Tuesday, STMicro led fallers, down 3 percent,while ams declined 2.7 percent and Infineon fell 2.4percent.

Risk appetite was poor across the board, as Europeaninvestors followed U.S. and Asian investors to the exit afterChina retaliated against U.S. tariffs.

"We believe that risk-reward for stocks has not turnedmedium-term negative, and would be adding at these levels,"wrote JP Morgan strategists in a note.

Equities have again entered "oversold" territory, they said,adding, however, that headwinds for technology stocks wereincreasing.

Outside the tech sector, food services group Sodexowas the worst-performer on the STOXX, down 3.8 percentafter Goldman Sachs (GS) cut the stock to "neutral". Sodexo hadalready suffered a 15.7 percent decline after warning on profitin the previous session.

"We now see the pick-up of competitive pressures is unlikelyto go away in the short term, while company profit continues tosuffer from intensifying labour inflation in the region," GSanalysts wrote.

Air France shares fell 3.2 percent after theairline said 75 percent of its flights would operate. The flagcarrier's unions called a strike for wage increases amid a widerlabour stoppage across France paralysing rail services.

Acquisition news also continued to move the European market.

Eurofins Scientific shares fell 2.9 percent, theworst performers on the STOXX, after the firm acquired LabFrontier in South Korea.

Italy's largest private broadcaster Mediaset nabbedthe top spot on the FTSE MIB index, up 6.9 percent,after signing a content-sharing deal with Sky's Italianunit and paving the way for a broader alliance.

Liberum analysts called the deal a "win-win".

"This agreement should be a TV advertising revenue boosteras it creates larger audiences," they wrote.

Berenberg upgraded Mediaset to a "buy", saying the dealmarked a "step change in profitability".

Basic resources and oil and gas stocks were a rare brightspot, making gains as metals prices rose.

(Reporting by Helen Reid; Editing by Kit Rees and Mark Potter)