The experimental static current-voltage <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> characteristics of almost ideal silicon p-n junctions are not adequately described by the classic Sah-Noyce-Shockley theory. The <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I-V</tex> characteristics are accurately modeled by admitting the presence of a new class of defects in addition to Shockley-Read-Hall generation-recombination centers. The new center, modeled as a donor-acceptor twin, behaves as a pure generation center.