A permeation routing algorithm is proposed which decides the detailed routes on a new layout model. The permeation router attains a higher density by using the expanded routing region as well as the conventional one simultaneously. This routing algorithm consists of two phases. One is to partition the trunk set into three subsets corresponding to the trunks to be routed in the channel on the lower transistor row, upper transistor row, or between transistor rows. The other is to route these channels by using the one-layer channel assignment method as well as the conventional one. The experiments show that the routing results are practical and that the processing time is proportional to the number of trunks to the power of 1.4.