Gate-pulse-induced recombination, known as charge pumping (CP), is a fundamental carrier recombination process, and has been utilized as a method for analyzing the electrical properties of defects (or dangling bonds) at the transistor interfaces, which is now recognized to be a well-matured and conventional method. Nevertheless, neither the origin (the bonding configuration) of the defects responsible for the CP nor their detailed recombination sequence has been clarified yet for Si metal-oxide-semiconductor (MOS) interfaces. In order to address these problems, we investigate the CP under spin resonance conditions at temperatures ranging from 27 to 300 K in Si(100) n type MOS transistors. We obtain evidence that P-b0 and E' centers, the two major dangling bonds at (and near) the Si(100) interface, participate in the CP recombination process. We also show that the spin-dependent CP process is explained by the formation of electron-electron spin pairs, which, in turn, reveals that the CP via P-b0 and E' centers is inherently a two-electron process.