In this paper, we measure the thermal conductivities (TCs) of Si 3 N 4 thin films prepared by lower pressure chemical vapor deposition with thickness ranging from 37 to 200 nm. The measurements were made at room temperature using a transient thermoreflectance technique. A three-layer model based on the transmission-line theory and the genetic algorithms were applied to obtain the TC of thin films and the interfacial thermal resistance (ITR). The results show that the value of the TC is 1.24-2.09 Wmiddotm -1 middotK -1 . The ITR between the metal layer and the thin film is about 1.2 times 10 -8 m 2 ldr K ldr W -1 . The estimated uncertainty of the TC is less than 18%.