The expansion of the market for wireless communications and sensors has led to the recent increase in demand for highly integrated MMICs for millimetre-wave wireless applications. These applications require MMICs that offer low cost, high integration, high functionality and high performance as well as simpler, more rapid development. An effective way of meeting these requirements and realising highly integrated MMICs is by employing multilayer three-dimensional (3-D) MMIC technology. The research work described in this thesis presents the modelling and characterisation of newly developed passive components such as coplanar waveguides (CPWs), thin-film microstrips (TFMSs) and transition transmission line structures using 3-D multilayer technology. These structures have been developed with low losses in mind, along with variable characteristic impedances and miniaturised size. With the knowledge obtained from the design and optimisation of CPW and TFMS transmission lines, new and improved compact CPW-to-TFMS transitions have been successfully achieved. Accurate electromagnetic modelling was carried out using the 2.5-dimensional ADS Momentum simulator. Newly improved fabrication techniques were employed to produce reported compact microwave components and circuits, in order to lower cost and simplify the process. Compact MMIC components were fabricated using a seven-layer fabrication procedure on semi-insulating GaAs substrate where pseudomorphic high electron mobility transistors (pHEMTs) pre-fabricated by the manufacturer. High frequency on-wafer RF measurements were carried out using Agilent 8510 series vector network analysers (VNAs). In-depth analysis and comparisons between the simulated and measured results are provided. Analysis of active MMIC components was achieved by developing small-signal equivalent circuits of the GaAs pHEMTs, and knowledge extracted from this analysis was employed in the development of large signal models of the pHEMT devices. Furthermore, the design and characterisation of a few MMIC circuits, such as limiters and amplifiers, demonstrates the integration of multilayer CPW passive components with prefabricated pHEMTs. These components are compatible with RF systems-on-chip sub-systems providing low cost, low loss performance with their ease of fabrication.