Methods of manufacturing a semiconductor device are provided. The method includes forming an isolation region in a substrate to define active regions extending in a single direction and being spaced apart from each other by the isolation region, forming a conductive layer in the isolation region and the active regions, etching the conductive layer to form bit line trenches extending in a first direction that is non-perpendicular to the single direction, forming bit line patterns in respective ones of the bit line trenches, etching the conductive layer to form a plurality of plug trenches two dimensionally arrayed along the first direction and a second direction perpendicular to the first direction, and filling the plug trenches with an insulation material to define conductive plug patterns in portions of the active regions. Related semiconductor devices are also provided.