The use of a p-n junction diode as a tool for the assessment of the p-well quality is demonstrated, by analyzing in detail the current-voltage and capacitance-voltage characteristics of n(+)-p-well junctions surrounded by either shallow trench isolation or polysilicon encapsulated local oxidation of silicon. As a reference, diodes fabricated in a p-type substrate and defined by a local oxidation of silicon isolation have been used. Particular emphasis is on the lifetime properties and leakage current activation energy of the p-well region, which has been fabricated by a deep (200 keV) and a shallow (55 keV) boron ion implantation. That the leakage current of large area diodes is governed by electric field-assisted generation of carriers from residual, unannealed deep B-implantation damage is demonstrated. The presence of such defects is confirmed by deep level transient spectroscopy analysis. The generation lifetime profile in the depletion region and the reverse current activation energy are extracted by taking account of the, electric field enhancement factor of the thermal generation. Finally, it is shown that the generation lifetime and residual defects depend mainly on the global thermal budget and little on the isolation scheme used.