A process for manufacturing a thin-film transistor device includes forming a dielectric insulation layer on a substrate, forming an amorphous silicon layer on the dielectric insulation layer, crystallizing the amorphous silicon layer, so as to obtain polycrystalline silicon, forming gate structures on the polycrystalline silicon, and forming first doped regions within the polycrystalline silicon laterally with respect to the gate structures. The crystallizing step includes forming first capping dielectric regions on the amorphous silicon layer, and then irradiating the amorphous silicon layer using a laser so as to form active areas of polycrystalline silicon separated by separation portions of amorphous silicon underlying the first capping dielectric regions.