A routing method of a semiconductor device includes steps (a) to (c). The step (a) checks a relation between a first interconnection pattern to be routed and a second interconnection pattern to be routed, wherein a line width of the second interconnection pattern is thicker than that of the first interconnection pattern. The step (b) refers to a routing rule of a design rule corresponding to a connection between the first interconnection pattern and the second interconnection pattern, when the first interconnection pattern and the second interconnection pattern would be routed in a same layer and connected each other. The step (c) routes the first interconnection pattern and the second interconnection such that the first interconnection is not bent in an area defined based on the routing rule.