Disclosed is a trench formation technique wherein an opening having a first sidewall with planar contour and a second sidewall with a saw-tooth contour is etched through a semiconductor layer and into a semiconductor substrate. Then, a crystallographic wet etch process expands the portion of the opening within the semiconductor substrate to form a trench. Due to the different contours of the sidewalls and, thereby the different crystal orientations, one sidewall etches faster than the other, resulting in an asymmetric trench. Also disclosed is a bipolar semiconductor device formation method that incorporates the above-mentioned trench formation technique when forming a trench isolation region that undercuts an extrinsic base region and surrounds a collector pedestal. The asymmetry of the trench ensures that the trench isolation region has a relatively narrow width and, thereby ensures that both collector-to-base capacitance Ccb and collector resistance Rc are minimized within the resulting bipolar semiconductor device.