A vertical multilayer transition for millimetre-wave frequencies is introduced and implemented in IMEC multi-chip module (MCM) technology. Simulation and measurement results for a back-to-back CPW-to-microstrip transition prototype show excellent agreement. Moreover, the microstrip-to-microstrip vertical via-less transition, as the core idea that is introduced, demonstrates less than 0.7 dB of loss in the band from 57 to 66 GHz, which satisfies the European as well as US standard bandwidth for 60 GHz communications systems. The low insertion loss along with the straightforward design procedure makes the proposed vertical via-less transition a valuable candidate for 60 GHz communications systems.Introduction: The millimetre-wave (MMW) frequency band has attracted much attention is recent years; not only because of the notable bandwidth available, but also the compactness capability in this band has been appealing to many researchers. To reach the demanding compactness factors in the MMW band, novel multilayer technologies have been developed for packaging and integration purposes. These technologies include multilayer printed circuit board (PCB) technology based on MMW-compatible laminates; low temperature co-fired ceramic (LTCC) and multi-chip module (MCM) thin film technology. In this Letter, IMEC's MCM technology [1] is used to fabricate a multilayer vertical transition useful in the measurement and packaging of active and passive devices in the MMW band. The term 'vertical' comes from the fact that in any of the aforementioned multilayer technologies, to reduce the area of the final product, the signals have to be brought from one layer to the other, vertically. The vertical transitions described in the literature can be categorised into two main groups: with-via and via-less. The first category is manufactured with technologies in which metalised vias are available [2][3][4][5]. However, in the MCM technology metalised vias in high resistive silicon are expensive and difficult to achieve. Therefore, via-less transitions are attractive from a practical point of view. Although there are via-less vertical transitions available in the literature [6,7], most of them have aperture-coupled geometries. In this Letter, a transition based on a broad-side coupler structure is introduced.