In the fast-moving electronics area, the studies of the germanium metal-insulator-semiconductor (MIS) devices are of wide interest. For the elaboration of the germanium MIS structures, alumina films with 2000 Angstrom thickness were deposited on thermally grown germanium oxide films as well as on clean germanium surfaces. The electrical measurements of Al2O3/Ge structures indicate a high density of states and consequently, a bad electronic quality of the MIS structures. On the other hand, we show that the presence of the germanium oxide layer GeO2 (30 Angstrom) between alumina and germanium reduces the density of states. This effect is due to the protection of the germanium surface during the deposition of alumina film and probably at the improvement of alumina adhesion. To improve the performances of our germanium MIS structures and to optimize the annealing conditions, we have employed 'forming-gas' [N-2 : H-2 = 85% : 15%] annealing of Al2O3/Ge and Al2O3:GeO2/Ge structures at different temperatures. After 30 min of annealing at T = 400 degrees C, the density of states at the interface has bran evaluated at 5 x 10(10) eV(-1) cm(-2).