Although the C-V profiling technique is usually applied to obtain the doping concentration of lightly doped wells, here we extend it to extract structural information of high-performance double poly bipolar transistors (BJTs) by comparing profiles taken from two adjacent but distinct C-V structures. In particular, the trenching that occurs in unprotected substrate silicon during the gate (base) poly overetch can be measured by the change in p + source/drain implant to n + buried layer depletion width for two such diodes, one with and one without trenching. The diffused extrinsic base junction depth of the double-poly BJT can be extracted similarly. Both of these physical dimensions must be accurately measured and tracked, to optimize bipolar device performance. Structural measurements by this comparative C-V technique are nondestructive, simple, and agree with scanning electron microscopy and secondary ion mass spectroscopy within approximately 100 angstrom (5%).