This monograph reports a research carried out to design monolithic microwave integrated circuit (MMIC) low pass filters using circuit and electromagnetic simulations. The filters were designed to be constructed on both Si and GaAs semiconductor wafers. The principal objectives were to reduce both circuit size and spurious content. Three types of designs are proposed here. The first is a Butterworth filter made of commensurate stubs, while the second filter is of the m-derived type. Both filters are realized using a single gold layer on the semiconductor substrate. The third filter uses a novel metal/polyimide/metal multilayer structure consisting of buried coplanar waveguide and polyimide overlay. Owing to the unique multilayer architecture, the filter operates well without spurious in the passband and stopband. The combination of several different materials in the structure also reduces the size. The proposed filter has stopband insertion and return losses of 20 dB and 25 dB respectively. A theoretical model to explain the new structure and design methodology are discussed in detail.