A spark-ignition internal-combustion engine, in particular of a supercharged and preferably a gasoline engine, is equipped with a system for variable actuation of the intake valves (7) including a pressurized fluid chamber (C) set between the intake valve (7) and the respective control cam, and an electrically actuated valve (24), the opening of which vents the aforesaid pressure chamber (C) so as to cause rapid closing of the valve (7), as a result of the respective elastic return means (9), even when the respective cam would tend to keep the valve open. The aforesaid variable-valve-actuation system is used in combination with control cams of the intake valves shaped in such a way as to generate an intake valve lift profile including a boot portion (C2) with substantially constant lift. The aforesaid boot portion is provided in the final part of the opening cycle of the intake valve, after BDC.
