The geometries of 48 isomers of SiHmPHn (m + n = 0-5), SiHmPHnSiHo (m + n + o = 0-7), and (SiH3)(3)P have been optimized at the MP2/6-31G(d) level of theory. Silylenes and cyclic structures dominate the compounds with low numbers of hydrogens; nevertheless, there are several examples of silicon-phosphorus multiple bonding. Relative energies, heats of formation, and bond dissociation energies have been calculated at the G2 level of theory. Two empirical schemes have been constructed to fit the atomization energies. A simple bond additivity approach reproduces the data with a mean absolute deviation of 5.3 kcal/mol. Better results are obtained with a group additivity scheme which gives a mean absolute deviation of 3.4 kcal/mol.