this invention provides a new configuration and manufacturing method of the hetero - junction bipolar transistor . according to the invention , the hbt comprises a semi - insulating inp substrate , a buffer layer on the substrate , a sub - collector layer , a collector layer , a base layer , an emitter layer , and an emitter contact layer these layers are sequentially grown on the buffer layer . since a pre - processing of forming two depressions in the sub - collector layer before growing the collector layer , the top surface of the emitter layer becomes planar surface . this results on the reduction of pits induced in the etching of the emitter contact layer , thus enhances the reliability and the high frequency performance of the hbt .