The paper introduces and considers two new classes of the so-called S-SDD \(_k(\sigma )\) and S-GSDD \(_k(\sigma )\) matrices, where S is a nonempty subset of the set \(R_A\) of strictly diagonally dominant rows of A, \(k\ge 1\) , and \(\sigma \in (0,\;1]\) is a real parameter. Properties of these matrices and their interrelations with some other matrix classes are considered. In particular, it is shown that S-SDD \(_k(\sigma )\) and S-GSDD \(_k(\sigma )\) matrices are nonsingular \({\mathcal {H}}\) -matrices and, moreover, SD-SDD and S-SSDD (Schur SDD) matrices. Based on the latter result, a general parameter-free upper bound for the \(l_\infty \) -norms of the inverses to S-SDD \(_k(\sigma )\) and S-GSDD \(_k(\sigma )\) matrices is obtained. Also upper bounds for \(\Vert A^{-1}\Vert _\infty \) based on a specific diagonal scaling of S-SDD \(_k(\sigma )\) and S-SDD \(_k(\sigma )\) matrices A, directly related to their definitions, are provided. Bibliography: 14 titles.