W-Si-N layers about 200 nm thick with different nitrogen content were reactively sputtered from a W5 Si3 target on oxidized silicon substrates. The thermal stability of the films' composition and resistivity was studied with ion beam analysis and four-point probe measurements. Upon vacuum annealing from 600 to 980 °C for 1.5 h, a sample with an initial 56 at. % of nitrogen gradually loses nitrogen down to 36%. This composition lies close to the W- Si3 N4 tie line. Concurrently, the room temperature resistivity decreases from 4.7 to about 2 mΩ cm. The composition changes only a little for a sample whose initial composition is near the W- Si3 N4 tie line and the resistivity changes significantly less than for the nitrogen-rich film. Interpretations are discussed. © 2006 American Institute of Physics.