This paper discusses some limitations in the approaches commonly adopted for device and circuit electro-thermal simulation. Thermal models for circuit simulation assume a simple geometry for the region where power dissipation occurs. Available models are compared. The impact of model parameters and bias condition on simulation accuracy is discussed. A new approach for calculating the temperature distribution under both steady-state and transient conditions is also proposed. The accuracy of two-dimensional (2D) electro-thermal device simulations is then investigated. It is shown that 2D simulations can lead to markedly inaccurate results. Possible approaches to overcome these limitations are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.