JAYSON WILLIAMS GOTTA DO AN EXTRA YEAR IN JAIL FOR HIS DWI!

Former NBA star Jayson Williams just got sentenced to a year behind bars for his DWI case ... but that sentence will have to wait until AFTER he finishes his current 5 years hard time for the shooting death of his limo driver.
Williams was arrested for DWI back in January after he slammed his Mercedes-Benz into a tree in New York City.

Moments ago in Manhattan Criminal Court, Williams -- through his lawyer -- plead guilty to DWI and was slapped with the 1-year sentence, and he also has to pay $16,643 for the tree he hit.

Less than two months after the DWI, Williams began serving his five year sentence for the 2002 limo driver shooting.