A submicron n-well SWAMI-LOCOS CMOS process on silicon substrate has been used for monolithic integration of an electrooptical system consisting of waveguides, photodetectors and VLSI CMOS circuits. The optical films have been deposited as SiON films on SiO2 buffer layers by LPCVD or PECVD technique, waveguides were delineated by plasma etching of the SiON film.