We present new results of the nucleosynthesis of s-elements in hot AGB stars. In the framework of the overshoot model, we show that the s-process nucleosynthesis depends sensitively on the thermodynamical conditions of the mixing zone and depending on the stellar mass and unknown overshoot parameter a large variety of s-process efficiencies can be found. We also provide a qualitative description of the production of s elements as a function of the stellar mass and metallicity. This mechanism could account for the large range of s-process efficiencies determined through the [Pb/Ce] values in low-metallicity stars.