Turbulence stabilization mechanisms in Internal Transport Barriers (ITBs) observed in tokamak plasmas are not fully understood. The turbulence is related to drift wave instabilities, which, although essentially electromagnetic in nature, are generally studied in the electrostatic approximation.Among the various instabilities associated to drift waves, those which seem to have a role in the formation of ITBs are instabilities driven by the ion and electron temperature gradients (respectively known as ITG and ETG modes). ITG modes, having longer wavelengths, can act on both ion and electron transport. On the contrary, ETG having shorter wavelengths, essentially modify only electron transport. Trapped Electron Modes (TEM), having wavelengths in the same range as those of ITG modes, represent another possibility of long wavelength instability. Several experiments in JET ion heated discharges show that the appearance of an ITB is linked to ITG mode stabilization.