The $2s$ photoionization and subsequent Auger transition cascade in atomic Si were studied by means of synchrotron-radiation-induced electron spectroscopy. After the $2s$ photoionization, the core hole states decay predominantly by a two-step Auger transition cascade into the triply ionized [Ne]$\mathit{nl}$ states. The ionization channels of the $2s$ core-ionized Si${}^{+}$ atoms to Si${}^{3+}$ ions were observed by measuring the conventional Auger electron spectra of the $L$${}_{1}$-$L$${}_{2,3}$$M$ Coster-Kronig transitions and the $L$${}_{2,3}$$M\ensuremath{-}\mathit{MMM}$ Auger transitions. The observed $L$${}_{1}$-$L$${}_{2,3}$$M$ and ${L}_{2,3}$$M\ensuremath{-}\mathit{MMM}$ Auger spectra were analyzed by means of extensive multiconfiguration Dirac-Fock computations. We found that the electron correlation plays a prominent role in the Auger cascade, especially for the final-step Auger $L$${}_{2,3}$$M$-$\mathit{MMM}$ spectrum. Additionally, it was seen that the ${L}_{2,3}$$M\ensuremath{-}\mathit{MMM}$ Auger spectrum of Si includes more Auger groups than the isoelectronic $L$${}_{2,3}$-$\mathit{MM}$ Auger spectrum of Al. Thus, more information on the intermediate ionic states is obtained if they are produced by Auger cascade rather than by direct photoionization.