A hermetic compressor for refrigeration systems, having a plurality of pistons of piezoelectric material (20) arranged within a hermetic shell (10), according to at least one sequential alignment and occupying, when in a first energizing condition, all of the corresponding internal volume of the hermetic shell (10). Each of the pistons (20) contracts relative to the same first lateral wall (14) of the hermetic shell (10) when in the second energizing condition, so as to have one of its end faces (21) distanced from the shell first lateral wall (14) in order to define the respective volume of fluid being compressed, which volume progressively decreases from the first to the last piston (20). An energizing means imparts electrical signals to the pistons (20) in a selective manner to establish each of the first and second energizing conditions, so as to cause the displacement and progressive compression of the initial volume of fluid admitted into the hermetic shell (10), from the inlet (11) to the outlet (12) of the hermetic shell (10).