All-solid-state batteries (ASSBs) were fabricated with alloy-anode composite (Li_3.25-Si + Li₂S-P₂S₅), sulfide-based glass electrolyte (Li₂S-P₂S₅), and sulfur-based composite cathode (S + Li₂S-P₂S₅ + C). When the anode was made of only lithium silicide, voltage noise occurred under 0.5-3.7 V cut-off condition, which is out of the electrochemical stability window of the solid electrolyte (SE). This result indicates that Li-dendrites were generated by irreversible Li-ion deposition at the limited interface between the anode and the SE due to oxidative decomposition of SE. We modified the anode to the composite structure consisting of lithium silicide + sulfide SE to increase the number of the alloying reaction site. The pyrolytic graphite sheet (PGS) was placed between the anode and the current collector to facilitate electron transport. As a result, the voltage noise did not occur under the 0.5-3.7 V cut-off condition. This study indicates that increasing the number of alloying reaction sites improves the structural stability of the full cell, thereby increasing the cycle life.