The Thunder 9 is a full-size semi-automatic handgun manufactured by Bersa at the Ramos Mejia production plant in Argentina.

This handgun is an evolution of the Model 90, the first full-size 9mm Luger pistol made by the Argentine company and introduced in 1989.

In 1994, when the entire Bersa pistol production line was renamed "Thunder", the Model 90 was modified with better functionalities and placement of the fire control group, match barrel, improved sights, better ergonomics, lighter weight and increased magazine capacity.

The magazine release button can be reversed for left-handed shooters and it has a "round in the chamber" indicator.

The pistol features ambidextrous safety, a decocker activated by the safety lever, emphasized sights, combat trigger guard, an integrated accessory mounting groove in the frame (added after the year 2000, in the Pro, for Professional, version), firing pin block; the pistol will not fire unless the trigger is squeezed all the way back protecting from accidental falling.

The Thunder Ultra Compact features a security key to activate a security locking system located on the left side of the frame under the take down lever, in the locked position the hammer cannot be cocked, the trigger won't work in double action, the slide won't cycle and the gun cannot be disassembled.