The first experimental spectroscopic study of the SiB and SiAl diatomic radicals is reported. Electron spin resonance results indicate that both molecules have X4SIGMA ground electronic states, in agreement with earlier theoretical calculations. The SiB and SiAl radicals were generated in neon matrices at 4 K by trapping the products produced from the pulsed laser vaporization of their alloys. Electronic structure information for these radicals is especially interesting given the utilization of silicon doped materials in semiconductor applications. The observed nuclear hyperfine interactions (A tensors) for B-10, B-11, and Al-27 in these molecular radicals were compared with the results of ab initio configuration-interaction theoretical calculations which were conducted as part of this experimental study. The neon matrix magnetic parameters (MHz) for (SiB)-B-11 are D = 800 (2), g (parallel-to) = 2.0014 (8), g(perpendicular-to) = 2.0005 (4), A(perpendicular-to) = 92.4 (5), and A(parallel-to) = 111(2). For (SiAl)-Al-27 the results (MHz) are D = 9 7 10 (2), g(parallel-to) = 1.9994(8), and g(perpendicular-to) = 1.997 8(4), \A(perpendicular-to)\ = 10.3(6), and \A(parallel-to)\ = 43.5 (8).