The microstructures of finely distributed Si-phases in $eta$-$FeSi_2$ thermoelectric matrix, were produced by heat-treating the melt-cast ingots of single $alpha$-$Fe_2Si_5$ phase at 730~85$0^{circ}C$ for 4~20 hours, or by resistance-hot-pressing the mechanically alloyed powders ordinarily consisting of $varepsilon$-FeSi and Si phases at 760~85$0^{circ}C$ for 10 minutes of composition. $(Fe_{0.98}Mn_{0.02})_xSi_2(x{leq$}1) The size and interspacing of dispersed Si-phases were able to control within a range of 0.05~0.27$mu extrm{m}$ and 0.2~0.6$mu extrm{m}$ by variations of heat treatment temperature and sintering temperature as well as the composition. respectively. The dispersion of Si- phases was expected to be effective for the reduction of thermal conductivity responsible for the increment of thermoelectric figure of merit.