Complementary LDMOS and MOS structures and vertical PNP transistors capable of withstanding a relatively high voltage may be realized in a mixed-technology integrated circuit of the so-called “smart power” type, by forming a phosphorus doped n-region of a similar diffusion profile, respectively in: The drain zone of the n-channel LDMOS transistors, in the body zone of the p-channel LDMOS transistors forming first CMOS structures; in the drain zone of n-channel MOS transistors belonging to second CMOS structures and in a base region near the emitter region of isolated collector, vertical PNP transistors, thus simultaneously achieving the result of increasing the voltage withstanding ability of all these monolithically integrated structures. The complementary LDMOS structures may be used either as power structures having a reduced conduction resistance or may be used for realizing CMOS stages capable of operating at a relatively high voltage (of about 20V) thus permitting a direct interfacing with VDMOS power devices without requiring any “level shifting” stages. The whole integrated circuit has less interfacing problems and improved electrical and reliability characteristics.