President Joe Biden's son is on trial in Delaware, where federal prosecutors previously indicted Hunter on gun charges. Hunter showed up at a Wilmington courthouse bright and early Monday, and jury selection is currently underway.

The Bidens are making history here ... Hunter's trial is the first ever involving the child of a sitting president.

As we reported, Hunter was indicted back in September on three counts related to gun possession while using narcotics.

HB is accused of filing a form claiming he was not using illegal drugs in October 2018 when he purchased a Colt Cobra revolver. He's also accused of being in possession of a firearm while using narcotics.

The exact charges include one count of False Statement in Purchase of a Firearm, one count of False Statement Related to Information Required to be Kept By Federal Firearms Licensed Dealer, and one count of Possession of a Firearm by a Person who is an Unlawful User of or Addicted to a Controlled Substance.

Hunter's trial is expected to play out in court over the next few weeks ... he's pled not guilty and is facing up to 25 years behind bars if convicted. Meanwhile, the White House has said POTUS won't pardon his son if a jury finds Hunter guilty.