A method of manufacturing a semiconductor device includes forming a lower structure including a plurality of transistors, forming a conductive layer on the lower structure, forming first preliminary pad mask patterns and wiring mask patterns on the conductive layer, forming pad mask patterns by patterning the first preliminary pad mask patterns while protecting the wiring mask patterns, and etching the conductive layer using the pad mask patterns and the wiring mask patterns as an etching mask to form pad patterns and wiring patterns.