CuSe and Cu3SbSe4 are two semiconductors with interesting electronic properties.To prepare useful samples, it is generally necessary to obtain precursor powders with good quality.Monodispersed morphology is for example important for densified ceramics with low porosity.In this work, we have developed a relatively simple and reproducible method, based on fast injection of reactants, to synthesize monodispersed nanoparticles.The size of these particles can be controlled simply by controlling the reaction time, as shown in figure 1 for CuSe as an example [1].The optical properties of these nanoparticles will be presented.large-scale synthesis of Cu3SbSe4 and related nanoparticles with a narrow size distribution will also be presented in this talk.Bulk materials have been prepared by hot-pressing [2].The thermoelectric properties of these materials will be discussed.