Summary: This paper describes a novel layout optimization technique using electromagnetic (EM) simulation. Simple equivalent circuits fitted to EM simulation results are employed in this method, to present a modification guide for a layout pattern. Fitting errors are also investigated with some layout patterns in order to clarify the applicable range of the method, because the errors restrict the range. The method has been successfully adopted to an X-band low noise MMIC amplifier (LNA). The layout pattern of the amplifier was optimized in only two days and the amplifier has achieved target performances--a 35 dB gain and a 1.7 dB noise figure--in one development cycle. The effective chip area has been miniaturized to 4.8 mm2. The area could be smaller than 70% in comparison with a conventional layout MMIC.