The effects of the physical implementation of the layout on the overall circuit behaviour is analysed for the output stage of a mobile phone power amplifier module and an FM radio tuner. For this purpose an equivalent circuit model is generated using a 2.5D BEM electromagnetic field solver. The most important feature of this EM simulation tool is that the number of components used to characterise the electromagnetic structure depends on the electrical size (i.e. ratio between feature size and wavelength), not geometrical complexity. This allows the electromagnetic analysis of for instance complete PCBs, whereas other 2.5D planar EM simulators are restricted to much smaller structures (i.e. small with respect to the minimum wavelength considered). The simulation results are compared with measurements. The results show that for the design of the output stage of the power amplifier layout effect simulation is crucial, while for the PCB regular circuit simulation is not enough to predict the actual circuit behaviour accurately above 100 MHz. The simulations including the EM layout effects show a good agreement with the measurements. Layout effect simulation can be used to optimize the circuit layout and reduce the design cycle.