A method of designing integrated circuits includes providing a design of an integrated circuit at a first scale, wherein the integrated circuit includes a shrinkable circuit including a first intellectual property (IP); and a non-shrinkable circuit including a second IP having a hierarchical structure. A marker layer is formed to cover the non-shrinkable circuit, wherein the shrinkable circuit is not covered by the marker layer. The electrical performance of the non-shrinkable circuit is simulated using a simulation tool, wherein the simulated non-shrinkable circuit is at a second scale smaller than the first scale.