UPDATE 1-Melexis hikes 2009 forecast after better Q3

* Q3 sales 35.9 mln euros vs expected 33 mln

* Raises 2009 sales forecast

* Forecasts 25 percent growth in 2010 (Adds details, background)

BRUSSELS, Oct 22 (Reuters) - Belgian semiconductor specialist Melexis (MLXS.BR) raised its 2009 sales forecast on Thursday after reporting better-than-expected third-quarter results and predicted 25 percent growth next year.

Melexis, whose semiconductors monitor oil pressure, control home lighting and regulate engine temperatures, said sales in the fourth quarter should be 40 million euros ($60.05 million), implying a full-year level of over 126 million.

The company had previously forecast 2009 sales at the top end of a 118-123 million euros range versus 185.5 million euros in 2008.

July-September revenues were 35.9 million euros, beating a 33 33 million euro average forecast from a Reuters poll of four analysts. That was down 26 percent on last year, but up 27 percent from the second quarter.

The company, which has around half its sales in the crisis-hit auto sector, said it expected sales to grow by 25 percent in 2010, assuming a euro/dollar rate of 1.45. The euro was just short of $1.50 on Thursday morning.

Melexis also said it agreed with its banks to obtain a covenant waiver for 62.5 million euros of its outstanding 70 million euros of debt. It added it expected to reach a similar deal for the remaining 7.5 million euros in the coming days.

Melexis designs and test chips, principally for the auto industry, but does not produce them. Its chief supplier is Xfab and its main customers are auto suppliers, TRW Automotive (TRW.N) and Sensata Technologies [BAINPS.UL] (Reporting by Philip Blenkinsop, Editing by Ian Geoghegan) ($1=.6697 Euro)