V-channel VMOS devices have been investigated from the point of view of fabrication process and their modelling. A fabrication process for p-channel VMOS devices having a wide range of channel lengths has been developed. Two new VMOS structures, namely a 'flat bottom VMOS' device and a depletion type p-channel VMOS device, have been introduced for the first time. The existing models of a planar MOS transistor and the VMOS transistor are briefly reviewed. The VMOS transistor model proposed by Holmes and Salama was checked for validity against the observed characteristics of p-channel devices fabricated in the laboratory and shown not to correlate with the observed device behaviour. A new VMOS device model based on the assumption of non-constant oxide charge density in the V-groove, as a consequence of the geometric structure, has been developed using conformal mapping techniques. This model shows a close correlation between calculated and measured device characteristics in the triode and saturation regions for p-channel MOS devices. A model for the n-channel VMOS transistor has also been proposed.