A MFI-based gallosilicate type catalyst is described.The catalyst is characterized by the following composition expressed by weight:a) 0.1 to 99.49% of a matrix,b) 0.5 to 99.99% of a zeolite having the following approximate chemical formula:M.sub.2/n O, Ga.sub.2 O.sub.3, xSiO.sub.2 whereinM represents a proton and/or a metallic cation,n is the valence of said cation,x is a number ranging from 12 to 1,00, the zeolite of MFI structure synthesized in a fluoride medium having a fluorine content ranging from 0.02 to 1.5% by weight incorporated during synthesis.The catalyst is notably used in aromatization reactions of light C.sub.2 -C.sub.4 gases in the presence or not of olefins.