The microcrystalline structure of (Bi1-xSbx)2Te3 (p-type) and (Bi1-xSex)2Te3 (n-type) solid solutions was studied using optical (OM) and scanning electronic microscopes (SEM), and was characterized by X-ray diffraction (XRD) and X-ray energy dispersive spectroscopy (EDS) in SEM. These semiconductor thermoelectric materials were obtained by the hot extrusion method, which is used in practical production of thermoelements. The extruded pieces were polycrystals with crystallite sizes 1–50 µm and 1–30 μm for p-type and n-type, respectively. SEM images showed that the crystallites of these extruded pieces had a nanocrystalline structure formed by nanocrystals and voids. The nanostructure morphology was studied using an artificial neural network (ANN). The p-type extrusions consisted of spherical nanocrystals with 10–100 nm dimensions, which formed the crystallites with dimensions up to 300 nm. The n-type extrusions consisted out of interwoven fibers of different orientation with up to 50 μm length and 20–200 nm diameters.