A high-voltage lateral MOSFET transistor structure constituted by various interdigitated modular elements formed on a layer of monocrystaline silicon is described together with a process for its fabrication.To save area of silicon and to reduce the specific resistivity RDS on doping drain regions are formed by implanting doping material in the silicon through apertures in the field oxide obtained with a selective anisotropic etching by utilizing as a mask the strips of polycrystaline silicon which serve as gate electrodes and field electrodes.