As the sole dominator of the commercial thermoelectric (TE) market, Bi2Te3‐based alloys play an irreplaceable role in Peltier cooling and low‐grade waste heat recovery. Herein, to improve the relative low TE efficiency determined by the figure of merit ZT, an effective approach is reported for improving the TE performance of p‐type (Bi,Sb)2Te3 by incorporating Ag8GeTe6 and Se. Specifically, the diffused Ag and Ge atoms into the matrix conduce to optimized carrier concentration and enlarge the density‐of‐states effective mass while the Sb‐rich nanoprecipitates generate coherent interfaces with little loss of carrier mobility. The subsequent Se dopants introduce multiple phonon scattering sources and significantly suppress the lattice thermal conductivity while maintaining a decent power factor. Consequently, a high peak ZT of 1.53 at 350 K and a remarkable average ZT of 1.31 (300–500 K) are attained in the Bi0.4Sb1.6Te0.95Se0.05 + 0.10 wt% Ag8GeTe6 sample. Most noteworthily, the size and mass of the optimal sample are enlarged to Ø40 mm‐200 g and the constructed 17‐couple TE module exhibits an extraordinary conversion efficiency of 6.3% at ΔT = 245 K. This work demonstrates a facile method to develop high‐performance and industrial‐grade (Bi,Sb)2Te3‐based alloys, which paves a strong way for further practical applications.