[en] The role of the current profile on drift wave stability is investigated using a linear electrostatic gyrokinetic code. Maximum growth rates linearly increases with R/L_t above a certain threshold R/L_c. A parametric study shows a dramatic stabilizing effect of negative magnetic shear, especially for large scale instabilities. In electron ITB (internal transport barrier) Tore-Supra discharges, negative magnetic shear stabilizes TEMs (trapped electron mode), whereas the steep electron temperature gradient (ETG) destabilizes ETG modes, which prevents electron heat transport from reaching neoclassical levels. (authors)