Semiconductor device having conductive layer within field oxide layer and method for forming the same

A method for forming a semiconductor device having a field oxide layer for isolating elements from each other, wherein the semiconductor device contains a field region and an active region, the active region having a junction region and a channel region, includes the steps of: a) providing a semiconductor structure having a trench in the field region; b) forming a first field insulating layer into the trench; c) forming a conductive layer on the first field insulating layer to fill a predetermined portion of the trench; and d) forming a second field insulating layer on the conductive layer to fill the remaining portion of the trench, thereby reducing an influence of an electric field caused by a potential difference between a semiconductor substrate and a junction region.