Cathodic electrodeposition of CdTe films was studied using aqueous ammonia-alkaline electrolytic baths (pH 10.7; temperature 343 K) in which Cd(II) and Te(IV) species were dissolved to form Cd(NH3)(4)(2+) and TeO32- ions, respectively. From the solution, 60 mM Cd(II)-10 mM Te(IV)-4.0 M NH3-1.0 M NH4+ (M = mol dm(-3)), a flat and smooth polycrystalline CdTe film (thickness, ca. 1 mu m) with nearly stoichiometric composition was deposited at a constant cathode potential, ranging from -0.70 to -0.30 V vs. SHE, whereas dendrite CdTe accompanying elemental cadmium was obtained at -0.80 V. The deposition behavior was fully explained by an underpotential deposition mechanism taking the calculated redox potentials of Te-0/(TeO32-)-O-IV and Cd-0/Cd-II(NH3)(4)(2+) pairs into consideration. During electrodeposition of nearly stoichiometric crystalline CdTe, the current density was decreasing monotonously.