in a method for manufacturing a bimos device , first and second semiconductor layers are formed on a semiconductor substrate , first and second field insulating layers are formed by using a locos process on said first and second semiconductor layers , respectively . the first field insulating layer partitions a bipolar transistor area and a mos transistor area , and the second field insulating layer is formed on a base - emitter junction region of the first semiconductor layer . then , impurities are introduced via the second field insulating layer into the first semiconductor layer to form a base region therein . then , an emitter opening is perforated in the second field insulating layer , and a polycrystalline silicon layer is formed on the second field insulating layer . then , impurities of a first conductivity type are introduced into the polycrystalline silicon layer , and a heating operation is performed upon the polycrystalline silicon layer to form an emitter region . then , the polycrystalline silicon layer is patterned to form an emitter electrode . then , a gate insulating layer is formed on the second semiconductor layer , and a gate electrode is formed on the gate insulating layer . finally , a base graft region is formed type in the first semiconductor layer and source / drain regions are formed in the second semiconductor layer .