An efficient method for the construction of 2,4‐diarylbenzo[4,5]thieno[3,2‐d]pyrimidines through the base‐promoted one‐pot three‐component tandem reactions of o‐nitrochalcones, benzamidine hydrochlorides, and elemental sulfur is described. The salient features of this protocol are the use of cheap and abundant sulfur source, readily available starting materials, transition‐metal‐free and mild conditions, satisfactory yield, and simple workup procedures. This transformation can also carry out on gram scale.