Sam Ronson -- Charged with DUI

Sam Ronson has been charged with misdemeanor DUI ... TMZ has learned -- this, after she was arrested last week while driving back from Las Vegas.

The San Bernardino County D.A. has charged Sam with two counts of DUI -- driving under the influence, and driving with a blood alcohol level over .08. The two charges are SOP.

If convicted, Sam faces a maximum of 6 months in jail and a $1,000 fine, but first offenders almost always get probation.