Detailed numerical assessment is given supporting the need to go beyond two-dimensions for numerically analyzing the electrothermal characteristics of power control devices employed in high-performance paralleling layout topology, and high-power microwave devices in monolithic microwave integrated circuits (MMIC). An accurate understanding of transient thermal characteristics, particularly the transient power-overload failure mechanism, is needed and requires the use of three-dimensional (3-D) transient electrothermal simulations. This will enable the design optimization of these power control devices for hardening against failure due to external fault conditions. We have compared the characteristic thermal speed response of Si, SiC, and GaN power control devices under short-circuit conditions, using 3-D time-dependent simulations. Such improved thermal simulation is also very important for high-power microwave devices and MMIC. Calibration of our numerical techniques with experiment is implemented using atomic force microscopy temperature measurements. The consistent agreement between measured values and simulated results indicates the need to couple detailed numerical simulation with high-resolution measurement technique, especially in identifying heat-flow bottlenecks. This will allow taking into account the actual thermal coupling of semiconductor substrate with the base plate and surrounding environment, where the fixed-temperature boundary condition usually applied at the substrate is not valid. (C) 2002 Elsevier Science Ltd. All rights reserved.