Abstract. This paper studies the effects of the substrate thermal gradients on the buffer insertion techniques. Using a non-uniform temperaturedependent distributed RC interconnect delay model, the buffer insertion problem is analyzed and design guidelines are provided to ensure the nearoptimality of the signal performance in the presence of the thermal gradients. In addition, the effect of temperature-dependent driver resistance on the buffer insertion is studied. Experimental results show that neglecting thermal gradients in the substrate and the interconnect lines can result in non-optimal solutions when using standard buffer insertion techniques and that these effects intensify with technology scaling.