The spatial confinement of phonons in semiconductor nanostructures affects the phonon dispersions and group velocities, resulting in suppression of lattice heat conduction in comparison with bulk materials. The reduced values of thermal conductivity were predicted for ultra-thin semiconductor nanolayers, nanowires, planar superlattices and cross-section-modulated nanowires [1-4]. Here we report on theoretical investigations of the lattice thermal conductivity in the Si-based segmented nanowires (SNs, also referred as 1D quantum dot superlattices) formed from Si, Ge and SiO2 quantum dots (QDs) of different size and shape. The phonon energy dispersions were calculated in the framework of the face-centered cubic cell model of lattice vibrations. The thermal flux and thermal conductivity in Si/SiO2 and Si/Ge SNs were obtained from the Boltzmann’s transport equation within the relaxation time approximation taking into account 1D density of phonon states and all basic mechanisms of phonon scattering: three-phonon Umklapp, boundary and impurity scatterings [2-3]. Cross-section modulation and acoustic mismatch between QDs in SNs leads to the exclusion of a part of phonons from thermal transport and to the significant reduction of lattice thermal conductivity. This effect is illustrated in Figure 1, where ratios between thermal fluxes in Si nanowire with 30x30 cross-section (all dimensions are in monolayers hereafter, 1 monolayer = 0.54 nm) and Si/SiO2 SNs are shown for SN #1 (QD1: 30x30x12; QD2: 30x30x12/38x38x12); SN #2 (QD1: 14x14x12; QD2: 14x14x12/18x18x12); SN #3 (QD1: 14x14x12; QD2: 14x14x12/26x26x12); SN #4 (QD1: 30x30x12/34x34x12; QD2: 30x30x12/38x38x12); SN #5 (QD1: 30x30x12/38x38x12; QD2: 30x30x12/46x46x12); SN #6 (QD1: 14x14x12/18x18x12; QD2: 14x14x12/22x22x12). The effect of QDs shape and size on the thermal conductivity was also studied. The strong suppression of lattice thermal conductivity in considered SNs demonstrate their potential in thermo-insulating and thermoelectric applications.