This study investigates the thermoelectric properties of W-doped p-type Ge0.9Sb0.1Te thermoelectricmaterials using the Single Parabolic Band (SPB) model and conducts an analysis aimed at optimizingperformance at room temperature. GeTe, a type IV-VI chalcogenide semiconductor, has gained attention asa mid-temperature (600 ~ 900 K) thermoelectric material. GeTe-based alloys are particularly utilized as ptypethermoelectric materials at high temperatures. However, pure GeTe contains a high concentration of Gevacancies, leading to a high hole concentration, a low Seebeck coefficient, and high thermal conductivity,which inherently limit its thermoelectric performance. In this study, the density-of-states effective mass (md*),non-degenerate mobility (μ0), weighted mobility (μW), and B-factor were calculated for Ge0.9-xWxSb0.1Te (x =0.01-0.05) composites with varying W doping levels (x). Based on the calculations, the theoretical maximumzT and the optimal carrier concentration were derived. Experimental results confirmed that the optimal Wdoping concentration for maximizing thermoelectric performance at 325 K is x = 0.05. At this composition,due to band convergence, md* reached its peak. Given that the suppression of μ0 was less pronounced relativeto the increase in md*, a maximum μW value was obtained. Additionally, the lattice thermal conductivity (κlat)was minimized, and the B-factor reached its peak. The theoretical maximum zT at this composition wasapproximately 0.91 when nH was optimized to 3.29 × 1019 cm-3, representing a 106.8% increase compared tothe pristine phase (Ge0.9Sb0.1Te, ~0.44) and a 295.7% increase compared to the x = 0.05 composition reportedby Bayikadi et al. (Ge0.85W0.05Sb0.1Te, ~0.23). And this suggests that this composition has the potential to beutilized not only for conventional high-temperature power generation but also for active cooling applications.