The Sheriff's Department tells TMZ Barron Hilton registered at nearly twice the legal limit, even for people over 21.
Spokesman Steve Whitmore tells us Barron blew a .14 blood alcohol reading.
In California, .08 is considered legally intoxicated for drivers over 21. If they're under 21 -- Barron is 18 -- any blood alcohol level is considered legally drunk.
In addition to the misdemeanor DUI charge, Hilton was also charged with carrying a false California driver's license. Whether the fake ID said he was over 21 or not is unknown at this time. His bail is set at $20,000. Chump change!